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.
Thomas Arendsen Hein <thomas@intevation.de> [Wed, 29 Mar 2006 12:45:33 +0200] rev 2015
Catch HTTPException when reading from remote http repository.
If the server dies very early, an httplib.IncompleteRead exception may be
raised, because httplib can't read a single byte. Catching all HTTPException
subclasses here will prevent ugly backtraces for similar things, too.