Allow short and long key ID user input in pgp_getkeybystr()

Allow short and long key ID user input in pgp_getkeybystr()

The following did not work, e.g. when leaving a key list, and at the "Sign as"
or "Encrypt to" prompt attempting to enter a key ID:
* set pgp_long_ids=no
  * enter a long key ID, with or without leading 0x
* set pgp_long_ids=yes
  * enter a short key ID without leading 0x

Specifically entering a long key ID should always be possible as evil32.com
has shown.

This also cleans up the logic used to determine the matching condition, which
was quite convoluted.. it even slightly speeds up the loop as less string
operations are involved in the inner condition.

This only changes how the result obtained from the pgp_* command line
interface is filtered.