Link with -lcrypto instead of -lssl when using openssl libraries.

Link with -lcrypto instead of -lssl when using openssl libraries.

Mark Allen had trouble with building GIT on his Darwin and
posted a patch to link with -lcrypto instead of -lssl on Darwin.
Later Daniel Barkalow suggested to change it for everybody who
uses openssl, because the relevant functionality is in -lcrypto
not in -lssl, and the current linking happens to work only
because -lssl pulls in -lcrypto.

Signed-off-by: Junio C Hamano <junkio@cox.net>