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.

Entry argument passed to git_index_add_frombuffer() should be const

gitignore: ignore vim swapfiles

Clear temporary buffer when filtering

If we are using a temporary buffer for filtering, be sure to clear
it before using it, in case the file that we are filtering is empty.

squash some leaks

Add a custom param to git_smart_subtransport_definition

WinHTTP for MinGW

note: use a git_buf to return the default namespace

examples: add remote example.

checkout: report correct invalid path

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

fix changelog

mkdir-ext: Assume directories don't exist; fix all race cases

win32 resource: allow custom comments field in DLL

Allow merges of files (and trees) with whitespace problems/fixes

The smart transport has already take the payload param. For the
sub transport a payload param is useful for the implementer.

clar: update to 08f434d

Update tips fixes

Lower case the include directive of windows header

PERF: In MERGE, lazily compute is_binary

Initialize refs vector in git_remote_update_tips().

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

The caller has otherwise no way to know how long the string will be
allocated or ability to free it.

This fixes #2944.

Add annotated versions of ref-modying functions

[WIP] Smarter pack-building