Merge branch 'bw/config-h'

Fix configuration codepath to pay proper attention to commondir
that is used in multi-worktree situation, and isolate config API
into its own header file.

* bw/config-h:
  config: don't implicitly use gitdir or commondir
  config: respect commondir
  setup: teach discover_git_directory to respect the commondir
  config: don't include config.h by default
  config: remove git_config_iter
  config: create config.h

builtin/commit.c

@@ -6,6 +6,7 @@
  */
 
 #include "cache.h"
+#include "config.h"
 #include "lockfile.h"
 #include "cache-tree.h"
 #include "color.h"