Need to check if tests are complete/sufficient, and test with multiple Pythons
and on Windows.

Changed zc.recipe.egg and the easy_install.scripts function into only adding
-S to scripts.

New package z3c.recipe.scripts and the easy_install.generate_scripts now
contains the more robust interpreter generation and the ability to
include site-packages.

Pertinent tests from the previous approach (from 3+ months ago) are
ported.  In the course of this port I discovered that big changes like
the ones in this checkin were needed.

an interpreter variant that supports all interpreter flags (AFAIK).  this commit contains core implementation (in easy_install module) and tests of all functionality except import_sitecustomize.  Integration into zc.recipe.egg and tests for import_sitecustomize (which will be more involved, and in tests.py) will follow.

this exposes the ability to request that site be imported in the ``script`` function. A later commit will expose this in the buildout configuration choices.

eliminate trailing spaces and normalize initial spacing of examples (some had five spaces, and the usual is four).

normalize text indentation, favoring not indenting expository text.  fix a few typos and spacing problems.

remove some superfluous whitespace, capitalize a comment, and normalize option error message to look like the ones in zc.buildout.

make a branch for the minor cleanup in gary-support-system-python branches.  this will be the base branch for my effort to break up the gary-support-system-python branch into five.

Revert to old style path.

- Incrementing didn't work properly when extending multiple files.
  https://bugs.launchpad.net/zc.buildout/+bug/421022

windows, urllib raises an invalid ioerror.