Fix memory leak when using hg commands over http repositories
When using hg commands over an http repository in a long running process, a
httphandler instance is leaked for each command, because of a loop
handler.parent -> OpenerDirector and OpenerDirector.handlers -> handler which
is not handled by Python's gc. Discussion on #mercurial concluded that removing
the __del__ method solved the problem.
adding a
abort: 'doesnotexist' not found in manifest!