Merge branch 'cc/no-gitk-build-dependency'

Merge branch 'cc/no-gitk-build-dependency'

Remove leftover bits from an earlier change to move gitk in its own
subdirectory.  Reimplementing the dependency tracking rules needs
to be done in gitk history separately.

* cc/no-gitk-build-dependency:
  Makefile: replace "echo 1>..." with "echo >..."
  Makefile: detect when PYTHON_PATH changes
  Makefile: remove tracking of TCLTK_PATH