No longer force use of /usr/bin/sort

In msysGit, the PATH contains the MSys paths before anything else,
so we can use "sort" (instead of "/usr/bin/sort"), just like git.git.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

check-builtins.sh

@@ -9,7 +9,7 @@ EOF
 } |
 make -f - sayIt 2>/dev/null |
 sed -n -e 's/.*XXX \(.*\) YYY.*/\1/p' |
-/usr/bin/sort |
+sort |
 {
     bad=0
     while read builtin