Cleanup initialization of libgcrypt.

* common/init.c (init_common_subsystems): Initialize libgcrypt.
* dirmngr/Makefile.am (dirmngr_ldap): Link with libgcrypt.

Most other modules already call gcry_check_version() after
init_common_subsystems() so may as well move initialization of libgcrypt
to here. Also fixes a warning in the system log from gpgconf --homedir.

• Signed-off-by: Ben Kibbey <bjk@luxsci.net>