Switch over to support for real IMAP sequence numbers (from A001 ->). Needed

Switch over to support for real IMAP sequence numbers (from A001 ->).  Needed
to fix my own function to only call sqimap_session_id() once!

Note: the old API is still there in its entirity, this is just another way to
call things.  With the changing sequence numbers though, any function working
with sqimap_session_id() must cache the result for testing against the
response of any command sent.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@2128 7612ce4b-ef26-0410-bec9-ea0150e637f0