allow cross-fork compares
allow cross-fork compares

Cross fork compare uses ':' to delineate "origin:branch" for cross-fork
comparisons.

matthewbauer/octokat.js,philschatz/octokat.js,matthewbauer/octokat.js,bitoiu/octokat.js,sanemat/octokat.js,sanemat/octokat.js,gmaclennan/octokat.js,philschatz/octokat.js,philschatz/octokat.js,gmaclennan/octokat.js,bitoiu/octokat.js