Fix fileID mess

Fix fileID mess

A few problems here:
* In e.g. keycodes.c the fileID field of the Info struct was never
  initialized to the id of the appropriate file, so it was always 0.
  There's some code which uses it, mostly for warnings.
* Some of the fileID fields were unsigned char, which overflows several
  times, seeing as the ID in some of our tests can get > 1000 (because
  we reuse the context).
* Some sign mismatches.
* fileID vs file_id.

Hopefully this fixes everything. I doubt this stuff had ever worked as
intended, in xkbcomp or otherwise.

Signed-off-by: Ran Benita <ran234@gmail.com>