#19 Bug in ga.query('ctlinfo')

[Rahul Mahajan]

In gacore.py, when ctlinfo is queried, it does not return the "levels" information for xlevs, ylevs and elevs, if the definition is "levels". This is because if the levels extend beyond the line of the definition, there is no ability to handle that. Attached is a bug-fix version to handle "levels". Please review, improve and include in the repository if found satisfactory.
Thanks.