Disable exception processing in XMPP close()

When re-establising a lost connection, it was causing an exception
before the XMPP connection is attempted, requiring a restart to
recovery.

Introduced by 16dc1265
Closes davesteele/cloudprint-service#9
Merge pull request #67 from davesteele/safe_close

Disable exception processing in XMPP close()
First functional include/exclude.
Code cleanup, documentation.
Documentation (and minor code cleanup).
Remove debug code.
Use -x from exclude.
Remove whitespace, response to comment from @armooo.
Catch exception for invalid regular expressions.
Merge pull request #71 from smblott-github/include-exclude

Include/exclude printers from export to GCP...
cloudprint.py: Log when get_rest() changes token
Remove alternate username/pw auth file format

... in preference for a sasl file with optional username/pw.
Add -u option to store username/password with sasl

The SASL token is timing out, in a period somewhere between days
and months. Optionally save the username and password in authfile,
in a format maintained by cloudprint.py, as a means to reauthenticate
in that case.

Closes #18 - saved password or pass to argument?
Closes #50 - Why 3 different authfile names, instead of 2? Causing errors?
Refresh XMPP authentication in process_jobs()

... if the username and password is known, to avoid problems with
the SASL token timing out.
Merge pull request #68 from davesteele/usercred

Optionally store user credentials for SASL refresh