Reduce size of profile.d-usrblackbox.sh to below 132 bytes.

Add test framework to make sure we don't break bash or sh.

tools/profile.d-usrblackbox-test.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+
+# Test profile.d-usrblackbox.sh
+
+# Make sure profile.d-usrblackbox.sh works.
+
+# Test variations including /usr/blackbox/bin is not in the path, is
+# already there in the front, middle, or end, and tests if the path has :
+# in weird places (front, middle, or both).
+
+# To run the test:
+# bash  tools/profile.d-usrblackbox-test.sh | fgrep --color /usr/blackbox/bin
+# sh  profile.d-usrblackbox-test.sh | fgrep --color /usr/blackbox/bin
+
+# NOTE: profile.d-usrblackbox.sh is written to be so small that it fits as an "inline" file.
+# https://lwn.net/Articles/468678/
+# To remove the last newline in the file:
+#  perl -i -pe 'chomp if eof' profile.d-usrblackbox.sh
+
+for p in \
+  '/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'                     \
+  '/usr/blackbox/bin:/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  '/usr/local/bin:/bin:/usr/blackbox/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  '/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/blackbox/bin'   \
+  '/Apple spaces/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  ; do
+
+  export PATH="$p"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH=":$p"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH="$p:"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH=":$p:"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+done

tools/profile.d-usrblackbox.sh

@@ -1,7 +1,6 @@
-# Prepend to $PATH.
-
-if type pathmunge > /dev/null 2>&1 ; then
-    pathmunge /usr/blackbox/bin
-elif ! echo $PATH | grep -Eq "(^|:)/usr/blackbox/bin($|:)" ; then
-    PATH=/usr/blackbox/bin:$PATH
-fi
+x=/usr/blackbox/bin
+if type pathmunge >/dev/null 2>&1;then
+pathmunge $x
+elif ! grep -sqF :$x:<<<":$PATH:";then
+PATH="$x:$PATH"
+fi