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

commit-graph.c

@@ -18,6 +18,7 @@
 #include "progress.h"
 #include "bloom.h"
 #include "commit-slab.h"
+#include "shallow.h"
 
 void git_test_write_commit_graph_or_die(void)
 {