give better error message on non-existent mapfile (issue813)
#!/bin/shhg initecho % should failhg add .hg/00changelog.imkdir aecho a > a/ahg ci -Amaln -s a becho b > a/becho % should failhg add b/becho % should succeedhg add becho % should still fail - maybehg add b/bexit 0