Fix to reflect selected branch for fork (#762)

PullRequestCtx.HeadInfo did not contain the current selected branch
causing issue #304

templates/repo/home.tmpl

@@ -10,7 +10,7 @@
 		<div class="ui secondary menu">
 			{{if .PullRequestCtx.Allowed}}
 				<div class="fitted item">
-					<a href="{{.BaseRepo.Link}}/compare/{{.BaseRepo.DefaultBranch}}...{{.PullRequestCtx.HeadInfo}}">
+					<a href="{{.BaseRepo.Link}}/compare/{{.BaseRepo.DefaultBranch}}...{{.Username}}:{{.BranchName}}">
 						<button class="ui green small button"><i class="octicon octicon-git-compare"></i></button>
 					</a>
 				</div>