agent: Fix passphrase cache lookups.
CACHE_MODE_ANY is supposed to match any cache mode except
CACHE_MODE_IGNORE, but the code used '==' to compare cache modes.
- agent/cache.c (cache_mode_equal): New function.
(agent_set_cache): Use the new function to compare cache modes.
(agent_get_cache): Likewise.
- tests/openpgp/Makefile.am (TESTS): Add new test.
- tests/openpgp/issue2015.scm: New file.
- GnuPG-bug-id: T2015
- Signed-off-by: Justus Winter <justus@g10code.com>