Fix the check for supports_pending_changesets
Fix the check for supports_pending_changesets

supports_pending_changesets is only defined in SCMTool, not Repository.

Reviewed at http://reviews.reviewboard.org/r/4276/

chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,brennie/reviewboard,KnowNo/reviewboard,1tush/reviewboard,1tush/reviewboard,custode/reviewboard,1tush/reviewboard,custode/reviewboard,beol/reviewboard,reviewboard/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,brennie/reviewboard,KnowNo/reviewboard,KnowNo/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,1tush/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,beol/reviewboard,beol/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,1tush/reviewboard,brennie/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,davidt/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,brennie/reviewboard,1tush/reviewboard,davidt/reviewboard,chipx86/reviewboard,1tush/reviewboard,beol/reviewboard,davidt/reviewboard,davidt/reviewboard,KnowNo/reviewboard,1tush/reviewboard,reviewboard/reviewboard