Merge branch 'hv/submodule-config'

The gitmodules API accessed from the C code learned to cache stuff
lazily.

* hv/submodule-config:
  submodule: allow erroneous values for the fetchRecurseSubmodules option
  submodule: use new config API for worktree configurations
  submodule: extract functions for config set and lookup
  submodule: implement a config API for lookup of .gitmodules values

diff.c

@@ -14,6 +14,7 @@
 #include "utf8.h"
 #include "userdiff.h"
 #include "sigchain.h"
+#include "submodule-config.h"
 #include "submodule.h"
 #include "ll-merge.h"
 #include "string-list.h"