When we fail to read from stdout, it's typically because the URL was
wrong and the server process has sent some output over its stderr
output.

Read that output and set the error message to whatever we read from it.

We set an error if we get an error when reading, but we don't bother
setting an error message for write failing. This causes a cryptic error
to be shown to the user when the target filesystem is full.

Now that `git_path_direach` lets us specify an error message to report,
set an appropriate error message while linking.

This function deals with functions doing IO which means the amount of
errors that can happen is quit large. It does not help if it always
ovewrites the underlying error message with a less understandable
version of "something went wrong".

Instead, only use this generic message if there was no error set by the
callback.

Fix MinGW build against openssl on maint/v0.22

Maintenance updates for v0.22

This was forgotten when the feature was implemented.

This mainly concerns mingw build.

Merge of pull request #3119 from ethomson/ignore as a single commit.

Conflicts:
	src/attr.c
	tests/attr/ignore.c

(also removed an unused member "has_regex" from all_iter)

Closes #2966.

The regcomp function returns a non-zero value if compilation of
a regular expression fails. In most places we only check for
negative values, but positive values indicate an error, as well.
Fix this tree-wide, fixing a segmentation fault when calling
git_config_iterator_glob_new with an invalid regexp.

When a commit is first set as unintersting and then pushed, we must take
care that we do not put it into the commit list as that makes us return
at least that commit (but maybe more) as we've inserted it into the list
because we have the assumption that we want anything in the commit list.

When walking backwards and marking parents uninteresting, make sure we
detect when the list of commits we have left has run out of
uninteresting commits so we can stop marking commits as
uninteresting. Failing to do so can mean that we walk the whole history
marking everything uninteresting, which eats up time, CPU and IO for
with useless work.

While pre-marking does look for this, we still need to check during the
main traversal as there are setups for which pre-marking does not leave
enough information in the commits. This can happen if we push a commit
and hide its parent.

git_checkout_tree() has some fallback behaviors for file systems
which don't have full support of filemodes.  Generally works fine,
but if a given file had a change of type from a 0644 to 0755 (i.e.,
you add executable permissions), the fallback behavior incorrectly
triggers when writing hte updated index.

This would cause a git_checkout_tree() command, even with the
GIT_CHECKOUT_FORCE option set, to leave a dirty index on Windows.

Also added checks to an existing test to catch this case.

Conflicts:
	src/checkout.c

When diffs are generated, the value for the 'nfiles' field of 'git_diff_delta'
will be consistent with the value in the 'status' field. Merging diffs can
modify the 'status' field of some deltas and the 'nfiles' field needs to be
updated accordingly.

Backports for the maint branch

Additional backports

In case of a bad url or other error during the connection setup, we
close the stream via free.

Otherwise, bailing out early when ls_to_vector() fails accesses
uninitialized memory.

Since the Linux platform has a case sensitive file system, the header name should be lower case for cross compiling purposes. (On Linux, the mingw header is called ```windows.h```).

When the user has a certificate check callback set, we still have to
check whether the stream we're using is even capable of providing a
certificate.

In the case of an unencrypted certificate, do not ask for it from the
stream, and do not call the callback.

While this is not even close to a fix, we can at least set an error
message so we know which error we are facing. Up to know we just
returned an error without a message.

This was but down to 5 when GitHub made a change to their server which
made them stop honouring the include-tag request.

This has recently been corrected, so we can bring it back up to six.

The user may decide to return any type of credential, including ones we
did not say we support. Add a check to make sure the user returned an
object of the right type and error out if not.

We want to ignore GIT_ENOTFOUND, but for that we need to capture the
error code from the reflog deletion.

If OpenSSL is disabled on Mac the SHA1 implementation goes
to the CommonCrypto from the system. In this case we should
not include the generic hash impl. Otherwise there would be
duplicated impls which fail the build.

Increment refcount of newly added cache entries just like existing
entries looked up from the cache. Otherwise the new entry can be
evicted from the cache and destroyed while it's still in use.

Fixes #2869. If included file includes more files, it may reallocate
cfg_file->readers, hence invalidate not only `r` pointer, but `result`
pointer as well.