Merge branch 'tb/shallow-cleanup'

Code cleanup.

* tb/shallow-cleanup:
  shallow: use struct 'shallow_lock' for additional safety
  shallow.h: document '{commit,rollback}_shallow_file'
  shallow: extract a header file for shallow-related functions
  commit: make 'commit_graft_pos' non-static

builtin/pack-objects.c

@@ -34,6 +34,7 @@
 #include "dir.h"
 #include "midx.h"
 #include "trace2.h"
+#include "shallow.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)