Merge branch 'jk/portable'

Merge branch 'jk/portable'

* jk/portable:
  t6000lib: re-fix tr portability
  t7505: use SHELL_PATH in hook
  t9112: add missing #!/bin/sh header
  filter-branch: use $SHELL_PATH instead of 'sh'
  filter-branch: don't use xargs -0
  add NO_EXTERNAL_GREP build option
  t6000lib: tr portability fix
  t4020: don't use grep -a
  add test_cmp function for test scripts
  remove use of "tail -n 1" and "tail -1"
  grep portability fix: don't use "-e" or "-q"
  more tr portability test script fixes
  t0050: perl portability fix
  tr portability fixes