fix bug in md5 code
use libgcrypt for MD5

This makes sure that CHAP authentication is disabled if the system
is running in FIPS 140-2 mode.  MD5 is not a secure algorithm according
to the standard.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Merge pull request #62 from bonzini/master

MD5 updates