Changes

Makefile: don't have contrib/windows in both DIST_SUBDIRS and
EXTRA_DIST
We used EXTRA_DIST of the entire directory to avoid listing all MSVC
files, and DIST_SUBDIRS for checking the version numbers in the windows
config files. Only use DIST_SUBDIRS (and list all files explicitly).
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>