Merge branch 'jk/cached-textconv'

* jk/cached-textconv:
  diff: avoid useless filespec population
  diff: cache textconv output
  textconv: refactor calls to run_textconv
  introduce notes-cache interface
  make commit_tree a library function

diff --cc Makefile
Simple merge

diff --cc commit.h
Simple merge

diff --cc diff.c
Simple merge