Merge https://github.com/j6t/git-gui

* https://github.com/j6t/git-gui:
  git gui: add directly calling merge tool from configuration
  git-gui: strip commit messages less aggressively
  git-gui: strip comments and consecutive empty lines from commit messages

diff --cc git-gui/lib/commit.tcl
Simple merge

diff --cc git-gui/lib/mergetool.tcl
Simple merge