git/commits: Test merge commits

Partially reverting ca82522 (git: do not include merges in the commit
range, 2017-03-21, #16).  I've kept the unrelated --no-pager addition
from that commit.

I think merges in the commit range should be checked against whatever
criteria the caller is asking for.  If the caller does not want to
check a machine-generated commit, they shouldn't include it in the
commit range.

And we already have special-cases for merges.  For example, we skip
DCO checks for merge commits.  I'd be happier without that special
case, because human-generated merge commits can still add novel code
(and therefore should have Signed-off-by), etc.  But I don't think we
want a blanket pass for merge commits.

Signed-off-by: W. Trevor King <[email protected]>

git/commits.go

@@ -12,7 +12,7 @@ import (
 // If commitrange is a git still range 12345...54321, then it will be isolated set of commits.
 // If commitrange is a single commit, all ancestor commits up through the hash provided.
 func Commits(commitrange string) ([]CommitEntry, error) {
-	cmdArgs := []string{"git", "--no-pager", "log", `--no-merges`, `--pretty=format:%H`, commitrange}
+	cmdArgs := []string{"git", "--no-pager", "log", `--pretty=format:%H`, commitrange}
 	if debug() {
 		logrus.Infof("[git] cmd: %q", strings.Join(cmdArgs, " "))
 	}