Merge branch 'jg/credential-cache-chdir-to-sockdir'

Merge branch 'jg/credential-cache-chdir-to-sockdir'

The "credential-cache" daemon process used to run in whatever
directory it happened to start in, but this made umount(2)ing the
filesystem that houses the repository harder; now the process
chdir()s to the directory that house its own socket on startup.

* jg/credential-cache-chdir-to-sockdir:
  credential-cache--daemon: change to the socket dir on startup
  credential-cache--daemon: disallow relative socket path
  credential-cache--daemon: refactor check_socket_directory