Allow searchin in the key listing also for mail addresses.

* src/keylist.c (search_keylist_function): Hack to search for a mail
address.

Due to a missing case insensitive strstr in glib the implemented search
is left-anchored. However, it is useful to search for mail addresses
and thus the search function now does a second left-anchored compare
after an open left angle.

• Signed-off-by: Werner Koch <wk@gnupg.org>