Fix a broken alias for SCons files.
Fix a broken alias for SCons files.

There was a broken alias for SCons files, resulting in an exception that
broke the diff viewer. The .sc alias was pointing to itself rather than .py.
It now points to the correct file type.

Fixes bug #1864

1tush/reviewboard,atagar/ReviewBoard,bkochendorfer/reviewboard,bkochendorfer/reviewboard,chipx86/reviewboard,chazy/reviewboard,atagar/ReviewBoard,chipx86/reviewboard,brennie/reviewboard,sgallagher/reviewboard,chazy/reviewboard,Khan/reviewboard,chazy/reviewboard,sgallagher/reviewboard,Khan/reviewboard,davidt/reviewboard,1tush/reviewboard,beol/reviewboard,brennie/reviewboard,atagar/ReviewBoard,1tush/reviewboard,chazy/reviewboard,Khan/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,brennie/reviewboard,atagar/ReviewBoard,chipx86/reviewboard,sgallagher/reviewboard,custode/reviewboard,custode/reviewboard,Khan/reviewboard,Khan/reviewboard,atagar/ReviewBoard,Khan/reviewboard,chazy/reviewboard,davidt/reviewboard,1tush/reviewboard,chazy/reviewboard,reviewboard/reviewboard,1tush/reviewboard,1tush/reviewboard,atagar/ReviewBoard,custode/reviewboard,1tush/reviewboard,chazy/reviewboard,bkochendorfer/reviewboard,beol/reviewboard,Khan/reviewboard,beol/reviewboard,custode/reviewboard,davidt/reviewboard,reviewboard/reviewboard,KnowNo/reviewboard,KnowNo/reviewboard,brennie/reviewboard,reviewboard/reviewboard,beol/reviewboard,KnowNo/reviewboard,davidt/reviewboard,atagar/ReviewBoard,chazy/reviewboard,1tush/reviewboard,Khan/reviewboard,1tush/reviewboard,KnowNo/reviewboard,Khan/reviewboard,atagar/ReviewBoard,chipx86/reviewboard,atagar/ReviewBoard,chazy/reviewboard,bkochendorfer/reviewboard