Fix git_checkout_tree() to do index filemodes correctly on Windows.

Fix for Issue #3023 tests fail with no network

Moved offending tests from network to online so they will get skipped
when there is a lack of network connectivity:
-test_online_remotes__single_branch
-test_online_remotes__restricted_refspecs

Attempt to fix Windows TLS memory leak.

Rebase fixes

Handle invalid multiline configuration

The idea...sometimes, a filemode is user-specified via an
explicit git_index_entry.  In this case, believe the user, always.

Sometimes, it is instead built up by statting the file system.  In
those cases, go with the existing logic we have to determine
whether the file system supports all filemodes and symlinks, and
make the best guess.

On file systems which have full filemode and symlink support, this
commit should make no difference.  On others (most notably Windows),
this will fix problems things like:
* git_index_add and git_index_add_frombuffer() should be believed.
* As a consequence, git_checkout_tree should make the filemodes in
the index match the ones in the tree.
* And diffs with GIT_DIFF_UPDATE_INDEX don't write the wrong filemodes.
* And merges, and probably other downstream stuff now fixed, too.

This makes my previous changes to checkout.c unnecessary,
so they are now reverted.

Also, added a test for index_entry permissions from git_index_add
and git_index_add_frombuffer, both of which failed before these changes.

`git_rebase_init` and `git_rebase_open` should take a
`git_rebase_options` and use it for future rebase operations on
that `rebase` object.

git_rebase_commit should return `GIT_EUNMERGED` when unmerged items
exist in the index, per the documentation.  Test that this is correct.

In `git_rebase_operation_current()`, indicate when a rebase has not
started (with `GIT_REBASE_NO_OPERATION`) rather than conflating that
with the first operation being in-progress.

Don't assume that comment chars are comment chars, they may be (an
attempt to be escaped).  If so, \; is not a valid escape sequence,
complain.

Combine unquoting and multiline detection to avoid ambiguity when
parsing.

Make sure to also update delta->nfiles when merging diffs

ignore: fix negative ignores without wildcards.

Implement git_submodule_set_branch.

Diff fixes

Fix memleak in test/core/mkdir reported by CRTDBG

revwalk: detect when we're out of interesting commits

Handle hide-then-push in the revwalk

Add memory leak detection/reporting using MSVC CRTDBG facility.

In the prior implementation, enabling GIT_DIFF_UPDATE_INDEX would overwrite
entries in the index with the ones generated from scanning the working if the
OID was the same.

Because this OID comparison ignores file modes, this means an file in the
workdir with only an exec bit difference with the one in the index would end
up being overwritten, resulting in the exec bit being loss. There might be
other related bugs but the fix of comparing OIDs and file modes should
address them all.

The variable noid is guaranteed to be zero at this point of the code path.

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.

As it seems it's not quite clear what it means to push a commit, try to
be more explicit about adding a new root and that we may not see this
commit if it is hidden.