[gyb] Provide Python 2 and 3 compatable exception syntax

In Python 2 the syntax to catch exceptions was:

except (Exception1, Exception2), target:

In Python 3 the syntax to catch exceptions is:

except (Exception1, Exception2) as target:

This newer Python 3 syntax is also available in 2.6 and 2.7. Therefore,
it is preferred for compatibility reasons. Additionally, the target no
longer can be a tuple. This patch refactors the exception handeling code
to be the newer Python 3 exception catch syntax.

Author: RLovelett

utils/gyb.py

@@ -138,7 +138,8 @@ def tokenizePythonToUnmatchedCloseCurly(sourceText, start, lineStarts):
                 if nesting < 0:
                     return tokenPosToIndex(tokenStart, start, lineStarts)
 
-    except tokenize.TokenError, (message, errorPos):
+    except tokenize.TokenError as error:
+        (message, errorPos) = error.args
         return tokenPosToIndex(errorPos, start, lineStarts)
 
     return len(sourceText)
@@ -327,7 +328,7 @@ def splitGybLines(sourceLines):
 
             lastTokenText,lastTokenKind = tokenText,tokenKind
 
-    except tokenize.TokenError, (message, errorPos):
+    except tokenize.TokenError:
         return [] # Let the later compile() call report the error
 
     if lastTokenText == ':':