[sharutils-4.11.1] Compilation warnings

When building shartuils-4.11.1 optimized to -O2 with GCC-4.7.2, I get these
warnings:

../lib/md5.c:117:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
../lib/md5.c:118:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
shar.c:2485:15: warning: variable ‘md’ set but not used [-Wunused-but-set-variable]

Following patches fixes it.

-- Petr