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/development/python-modules/generic/wrap.sh

@@ -26,7 +26,7 @@ wrapPythonProgramsIn() {
     done
 
     # Find all regular files in the output directory that are executable.
-    for f in $(find "$dir" -type f -perm /0100); do
+    for f in $(find "$dir" -type f -perm -0100); do
         # Rewrite "#! .../env python" to "#! /nix/store/.../python".
         if head -n1 "$f" | grep -q '#!.*/env.*\(python\|pypy\)'; then
             sed -i "$f" -e "1 s^.*/env[ ]*\(python\|pypy\)^#! $python^"