Add empty repo test

tests/test-empty

@@ -0,0 +1,7 b''
+#!/bin/sh
+
+hg init
+hg log
+hg grep wah
+hg manifest
+hg verify

tests/test-empty.out

@@ -0,0 +1,5 b''
+checking changesets
+checking manifests
+crosschecking files in changesets and manifests
+checking files
+0 files, 0 changesets, 0 total revisions