Fill the pointers for matching refspecs

Tackle remote API issues from bindings

These are updates, same as the rest, we should call this callback. As we
are using the callback, let's make sure to skip unnecessary updates.

When we moved from acting on the instance to acting on the
configuration, we dropped the validation of the passed refspec, which
can lead to writing an invalid refspec to the configuration. Bring that
validation back.

An anonymous remote is not configured and cannot therefore have
configured refspecs. Remove the parameter which adds this from the
constructor.

Fix ident replacement to match Git behavior

Git inserts a space after the SHA1 (as of 2.1.4 at least), so do the
same.

Thin packs: don't 

When thickening a pack, avoid loading already loaded bases and
trying to insert them all over again.

When creating an index, know that we do not have an index for
our own packfile, preventing some unnecessary file opens and
error reporting.

openssl: don't try to handle WANT_READ or WANT_WRITE

When we look for which remote corresponds to a remote-tracking branch,
we look in the refspecs to see which ones matches. If none do, we should
abort. We currently ignore the error message from this operation, so
let's not do that anymore.

As part of the test we're writing, let's test for the expected behaviour
if we cannot find a refspec which tells us what the remote-tracking
branch for a remote would look like.

When we find out that we're dealing with a matching refspec, we set the
flag and return immediately. This leaves the strings as NULL, which
breaks the contract.

Assign these pointers to a string with the correct values.

Fix error when building as C++.

index_add_all: include untracked files in new subdirs

No need to get reports about individual ignored files, having a
single ignored directory delta is enough.

ignore: clear the error when matching a pattern negation

When we discover that we want to keep a negative rule, make sure to
clear the error variable, as it we otherwise return whatever was left by
the previous loop iteration.

Our doc parser really wants the types to be declared in the header it's
reading.

Improve server error reporting

This can be used by tools to show mesages about failing to communicate
with the server. The error message in this case will often contain the
server's error message, as far as it managed to send anything.

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.

Use a diff for iteration in index_update_all and index_add_all

Provide error messages for git_path_direach operations

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.

These were left over from the culling as it's not clear which use-cases
might benefit from this. It is not clear that we want to support any
use-case which depends on changing the remote's idea of the base
refspecs rather than passing in different per-operation refspec list, so
remove these functions.

The code used to rely on the clone code calling the remote's save, which
does not happen anymore, meaning that the configuration settings the
remote expected were not being written to disk.

The run-time configuration was still being affected, so the right branch
was being cloned. The tests continued to pass as we did not check for
the configuration entires. Fix this by creating the remote with the
single-branch refspec we want and checking for its existence in the
configuration.

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.

Updated dlibgit link.

Bring Early EOF message in line with the other two