Need a way to ignore all undefined flags

[GoogleCodeExporter]

Currently, when gflags module sees an unrecognized flag, it throws an exception 
and give up processing.  Even if we catch the exception and ignore it, we end 
up with a half baked flag registry.

The option "undefok" does part of the work, but it works only on specifically 
whitelisted flags.  It would be great to have an option to have it ignore ALL 
unrecognized flags.

Original issue reported on code.google.com by linshu...@google.com on 22 Mar 2012 at 5:29