fix backtrace printed when cannot get lock.
change lock error handling code so exceptions have useful info and
exception handling in one place.
add test case for when cannot get lock.
abort: Connection refused
255
copy: No such file or directory
changeset: 0:53e17d176ae6
tag: tip
user: test
date: Mon Jan 12 13:46:40 1970 +0000
summary: test
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
foo
pulling from old-http://localhost:20059/remote
searching for changes
no changes found