added check for legal xml attribute names

As of right now, it doesn't try to fix the name or make it legal, it just includes illegal variable names as a line of log text instead of as an attribute.  I can do something more sophisticated later if we decide we need it.

Once you accept this pull request (and then pull it down to atlacamani) you'll need to rerun starlab.kiraout_to_xml() for each of the affected runs.