Distinguish between wireshark *source files* and wireshark *dependencies*.

Only the former should be run through checkAPI.pl; Windows .rc files,
for example, shouldn't.

Change-Id: I948705b4020b413834c37a0d685eedcb747aa237
Reviewed-on: https://code.wireshark.org/review/3303
Reviewed-by: Guy Harris <guy@alum.mit.edu>