wildmatch: rename constants and update prototype

wildmatch: rename constants and update prototype

- All exported constants now have a prefix WM_
- Do not rely on FNM_* constants, use the WM_ counterparts
- Remove TRUE and FALSE to follow Git's coding style
- While at it, turn flags type from int to unsigned int
- Add an (unused yet) argument to carry extra information
  so that we don't have to change the prototype again later
  when we need to pass other stuff to wildmatch

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>