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.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