added line to validate comet name

Added a line to disallow comet names that have a number in the second position in order to avoid having parse_comet() incorrectly interpret input like "2015XN77" as a well-formed comet designation (where number=2015, type=X, and name=N77)

Author: hhsieh00

sbpy/data/names.py

@@ -436,6 +436,9 @@ def parse_comet(s):
                 if len(el[5]) > 0:
                     if len(el[5]) > 1:
                         r['name'] = el[5]
+                        if r['name'][1].isdigit():
+                            raise TargetNameParseError('{} does not appear to be a '
+                                                       ' comet identifier'.format(s))
 
         if len(r) == 0 or 'type' not in r:
             raise TargetNameParseError(('{} does not appear to be a '