Merge branch 'tz/credential-authinfo'

A new read-only credential helper (in contrib/) to interact with
the .netrc/.authinfo files.  Hopefully mn/send-email-authinfo topic
can rebuild on top of something like this.

* tz/credential-authinfo:
  Add contrib/credentials/netrc with GPG support

Author: gitster

contrib/credential/netrc/Makefile

@@ -0,0 +1,5 @@
+test:
+	./test.pl
+
+testverbose:
+	./test.pl -d -v