Fail on unmodified deltas when they're unexpected
Fix bug marking submodule diffs as unmodified

There was a bug where submodules whose HEAD had not been moved
were being marked as having an UNMODIFIED delta record instead
of being left MODIFIED.  This fixes that and fixes the tests to
notice if a submodule has been incorrectly marked as UNMODIFIED.
Merge pull request #1684 from libgit2/fix-dirty-submodule-diff

Dirty submodules do not correctly appear in diffs
Test submodules with empty index or orphaned head

In both of these cases, the submodule data should still be loaded
just (obviously) without the data that comes from either the index
or the HEAD.

This fixes a bug in the orphaned head case.
Merge pull request #1688 from arrbee/submodule-load-ignore-orphaned-head

Test submodules with empty index or orphaned head
Fix compilation warnings
test: Fix memory leak
Merge pull request #1690 from nulltoken/fix/warnings

Fix Win32/64 compilation warnings & memory leak
Fix docs to use proper enum names that exist.
Merge pull request #1694 from AndrejMitrovic/FixupDocEnums

[trivial] Fix docs to use proper enum names
Fix small typo in docs for git_repository_message.
Merge pull request #1696 from AndrejMitrovic/FixTypo

[trivial] Fix small typo in docs for git_repository_message.
Fix segfault in git_status_foreach_ext()

Add tests for the `GIT_STATUS_SHOW_XXX` flags.
Merge pull request #1701 from yorah/fix/gh-1698

Fix segfault in git_status_foreach_ext()