settle on "include-site-packages" and migrate all variations of "add-site-packages" to that spelling.

integrate ability to control what eggs are accepted from site-packages into z3c.recipe.scripts.  Without this, the ability to use z3c.recipe.scripts without site-packages was broken.

this is now the branch for my site-packages changes.  It is merged with trunk.  The zc.recipe.egg recipe returns to being fully backward compatible; if you want to use a system Python, use the z3c.recipe.scripts recipe for scripts and interpreter.

the whitespace-police, the typo-police, the grammar police, and the Windows testing police all joined together for this check-in of mostly trivial changes.