Merge branch 'ab/t0051-skip-on-non-windows'

Conditional test update.

* ab/t0051-skip-on-non-windows:
  t0051: use "skip_all" under !MINGW in single-test file

t/t0051-windows-named-pipe.sh

@@ -3,8 +3,13 @@
 test_description='Windows named pipes'
 
 . ./test-lib.sh
+if ! test_have_prereq MINGW
+then
+	skip_all='skipping Windows-specific tests'
+	test_done
+fi
 
-test_expect_success MINGW 'o_append write to named pipe' '
+test_expect_success 'o_append write to named pipe' '
 	GIT_TRACE="$(pwd)/expect" git status >/dev/null 2>&1 &&
 	{ test-tool windows-named-pipe t0051 >actual 2>&1 & } &&
 	pid=$! &&