Merge branch 'tz/cred-netrc-cleanup'

Merge branch 'tz/cred-netrc-cleanup'

Build and test procedure for netrc credential helper (in contrib/)
has been updated.

* tz/cred-netrc-cleanup:
  git-credential-netrc: make "all" default target of Makefile
  git-credential-netrc: fix exit status when tests fail
  git-credential-netrc: use in-tree Git.pm for tests
  git-credential-netrc: minor whitespace cleanup in test script