* call-scd.c: Seirialized all scdaeom access when using Pth.
* cache.c: Made the cache Pth-thread-safe.
(agent_unlock_cache_entry): New.
* findkey.c (unprotect): Unlock the returned cache value.
* command.c (cmd_get_passphrase): Ditto.
* gpg-agent.c (main): Register pth_read/write with Assuan.