Slightly better message for some unsupported input

This is not perfect yet, but a slight improvement for input variants of
a type we don't support. Fixes for example #375

mutalyzer/mapping.py

@@ -341,6 +341,8 @@ class Converter(object) :
         for mutation in mutations:
 
             if not mutation.StartLoc :
+                self.__output.addMessage(__file__, 4, 'EUNKNOWN',
+                                         'Variant type not supported.')
                 return None
 
             # Get the coordinates of the start position

mutalyzer/variantchecker.py

@@ -989,7 +989,7 @@ def process_raw_variant(mutator, variant, record, transcript, output):
         # All non-EX positioning ways need a start location.
         # Todo: Better message.
         output.addMessage(__file__, 4, 'EUNKNOWN',
-                          'An unknown error occurred.')
+                          'Variant type not supported.')
         raise _RawVariantError()
 
     elif variant.StartLoc.IVSLoc: