Fix "irc" module naming conflict with python-2.7.

Using "from irc import ..." in module named "irc" causes python-2.7 to
try to re-use __module__ in that import, and not look it up in sys.path.

Fix is to force such lookup via "imp.find_module".
Any ImportError (either missing "imp" or other "irc" modules) should be
treated same as before, causing a fatal error.
Use password (as PASS) in irc backend.

Was silently discarded previously.