Merge branch 'pt/credential-xdg'

Tweak the sample "store" backend of the credential helper to honor
XDG configuration file locations when specified.

* pt/credential-xdg:
t0302: "unreadable" test needs POSIXPERM
t0302: test credential-store support for XDG_CONFIG_HOME
git-credential-store: support XDG_CONFIG_HOME
git-credential-store: support multiple credential files

diff --cc credential-store.c
Simple merge