query and show commits by branch

This allows the same SHA to have different builds on different branches, each
separately viewable. This is useful for expressing a "pipeline" in terms of
branches, e.g. a commit starts on branch A and progress through B and C to
master, with the build script switching on branch name.

Previously viewing each build would arbitrarily choose which branch's commit
to show.

pkg/handler/builds.go

@@ -9,11 +9,12 @@ import (
 
 // Returns the combined stdout / stderr for an individual Build.
 func BuildOut(w http.ResponseWriter, r *http.Request, u *User, repo *Repo) error {
+	branch := r.FormValue(":branch")
 	hash := r.FormValue(":commit")
 	labl := r.FormValue(":label")
 
 	// get the commit from the database
-	commit, err := database.GetCommitHash(hash, repo.ID)
+	commit, err := database.GetCommitBranchHash(branch, hash, repo.ID)
 	if err != nil {
 		return err
 	}