Merge branch 'sg/test-i18ngrep' into maint

Test fixes.

* sg/test-i18ngrep:
  t: make 'test_i18ngrep' more informative on failure
  t: validate 'test_i18ngrep's parameters
  t: move 'test_i18ncmp' and 'test_i18ngrep' to 'test-lib-functions.sh'
  t5536: let 'test_i18ngrep' read the file without redirection
  t5510: consolidate 'grep' and 'test_i18ngrep' patterns
  t4001: don't run 'git status' upstream of a pipe
  t6022: don't run 'git merge' upstream of a pipe
  t5812: add 'test_i18ngrep's missing filename parameter
  t5541: add 'test_i18ngrep's missing filename parameter

diff --cc t/test-lib-functions.sh
Simple merge