Merge branch 'jc/undash-in-tree-git-callers'

Merge branch 'jc/undash-in-tree-git-callers'

A handful of places in in-tree code still relied on being able to
execute the git subcommands, especially built-ins, in "git-foo"
form, which have been corrected.

* jc/undash-in-tree-git-callers:
  credential-cache: use child_process.args
  cvsexportcommit: do not run git programs in dashed form
  transport-helper: do not run git-remote-ext etc. in dashed form