tests/test-install.t

localrepo: add ignoremissing parameter to branchtip

Previously, in the namespaces api, the only caller of branchtip was singlenode
which happened to raise the same exception that branchtip raised: KeyError.

This is a minor change but will allow upcoming patches to use repo.branchtip to
not raise an exception if a branch doesn't exist. After that, it will be
possible for extensions to use the namespace api in a stable way.

hg debuginstall
  $ hg debuginstall
  checking encoding (ascii)...
  checking Python executable (*) (glob)
  checking Python version (2.*) (glob)
  checking Python lib (*lib*)... (glob)
  checking installed modules (*mercurial)... (glob)
  checking templates (*mercurial?templates)... (glob)
  checking commit editor...
  checking username...
  no problems detected

hg debuginstall with no username
  $ HGUSER= hg debuginstall
  checking encoding (ascii)...
  checking Python executable (*) (glob)
  checking Python version (2.*) (glob)
  checking Python lib (*lib*)... (glob)
  checking installed modules (*mercurial)... (glob)
  checking templates (*mercurial?templates)... (glob)
  checking commit editor...
  checking username...
   no username supplied
   (specify a username in your configuration file)
  1 problems detected, please check your install!
  [1]