Merge branch 'dl/credential-cache-socket-in-xdg-cache'

The default location "~/.git-credential-cache/socket" for the
socket used to communicate with the credential-cache daemon has
been moved to "~/.cache/git/credential/socket".

* dl/credential-cache-socket-in-xdg-cache:
  credential-cache: add tests for XDG functionality
  credential-cache: use XDG_CACHE_HOME for socket
  path.c: add xdg_cache_home

cache.h

@@ -1176,6 +1176,13 @@ extern int is_ntfs_dotgit(const char *name);
  */
 extern char *xdg_config_home(const char *filename);
 
+/**
+ * Return a newly allocated string with the evaluation of
+ * "$XDG_CACHE_HOME/git/$filename" if $XDG_CACHE_HOME is non-empty, otherwise
+ * "$HOME/.cache/git/$filename". Return NULL upon error.
+ */
+extern char *xdg_cache_home(const char *filename);
+
 /* object replacement */
 #define LOOKUP_REPLACE_OBJECT 1
 #define LOOKUP_UNKNOWN_OBJECT 2