Add status test for long paths
Don't use win32-only macro in test code
Add long-file-name branch to test repo
Add checkout test for long file name
Add typedefs for win32 utf-8 and utf-16 buffers

...and normalize the signatures of the two conversion functions.
Rename git_win_str_utf* to git_win32_path_utf*
Discriminate path-specific and general UTF-X conversions
Niggles, fix ming2 cross-compile