mass rewrite of find parameters to cross-platform style

Fixes #9044, close #9667. Thanks to @taku0 for suggesting this solution.
Now we have no modes starting with `/` or `+`.

Rewrite the `-perm` parameters of find:
 - completely safe: rewrite `/0100` and `+100` to `-0100`,
 - slightly semantics-changing: rewrite `+111` to `-0100`.
I cross-verified the `find` manual pages for Linux, Darwin, FreeBSD.

pkgs/applications/science/math/mathematica/9.nix

@@ -86,7 +86,7 @@ stdenv.mkDerivation rec {
 
   preFixup = ''
     echo "=== PatchElfing away ==="
-    find $out/libexec/Mathematica/SystemFiles -type f -perm +100 | while read f; do
+    find $out/libexec/Mathematica/SystemFiles -type f -perm -0100 | while read f; do
       type=$(readelf -h "$f" 2>/dev/null | grep 'Type:' | sed -e 's/ *Type: *\([A-Z]*\) (.*/\1/')
       if [ -z "$type" ]; then
         :