Fix #152: Properly check for loop in serf wait chain
data: Separate data file access into data_source_dos.c

This separates the data file access from the graphics functions and allows
other data sources to be added in the future.
data_source_dos: Fix weird comment indentation
Merge branch 'wdigger-backend'

Separate data file access into data_source_dos.c
Consistently use dashes in file names

Rename version_vcs.h and data_source_dos.c to version-vcs.h and
data-source-dos.c. freeserf_endian.h is kept as it is, as "freeserf_" is
just a prefix to avoid clashing with system headers.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Makefile.am