insert pth eggs at index of site-packages they come from

thx Rok Garbas!

svn path=/nixpkgs/branches/stdenv-updates/; revision=32584

pkgs/development/python-modules/site/site.py

@@ -45,6 +45,7 @@ def __boot():
     sys.__egginsert = 0                     # and reset the current one
 
     for item in PYTHONPATH:
+        sys.__egginsert = sys.path.index(os.path.abspath(item))
         addsitedir(item)
 
     sys.__egginsert += oldpos           # restore effective old position