This should make things slightly more consistent and unambiguous, and
the stdint types are already used here and there (in loaders).
I'm not aware of any systems where this change makes any difference.
If there are targets out there with 64 bit ints imlib2 might now work
there and on targets with 16 bit ints it most likely still doesn't.
- Always include config.h before Imlib2.h
Needed for X_DISPLAY_MISSING.
- Always include config.h and Imlib2.h first
Should make it more likely to spot stuff missing but required
in Imlib2.h, like stddef.h.
gtest.h apparently must be included before X headers though.
- Make sure we use the Imlib2.h here and not the one in /usr/include
Also ensure that the tests build when building without X.