Add some comments

Author: lunny

routers/api/v1/repo/pull.go

@@ -1057,6 +1057,7 @@ func MergePullRequest(ctx *context.APIContext) {
 	}
 	log.Trace("Pull request merged: %d", pr.ID)
 
+	// for agit flow, we should not delete the agit reference after merge
 	if form.DeleteBranchAfterMerge && pr.Flow == issues_model.PullRequestFlowGithub {
 		// check permission even it has been checked in repo_service.DeleteBranch so that we don't need to
 		// do RetargetChildrenOnMerge

routers/web/repo/pull.go

@@ -1403,7 +1403,7 @@ func CleanUpPullRequest(ctx *context.Context) {
 
 	pr := issue.PullRequest
 
-	// Don't cleanup unmerged and unclosed PRs
+	// Don't cleanup unmerged and unclosed PRs and agit PRs
 	if !pr.HasMerged && !issue.IsClosed && pr.Flow != issues_model.PullRequestFlowGithub {
 		ctx.NotFound("CleanUpPullRequest", nil)
 		return