easy_install APIs.

- Added an eggs recipe that *just* installes eggs.

- Advertized the scripts recipe for creating scripts.

Updated some tests to deal with the fact that setuptools eggs keep
oscillating between being files and directories.

These are used and tested indirectly in various ways.

----------

- https://bugs.launchpad.net/products/zc.buildout/+bug/71246

Buildout extensions installed as eggs couldn't be loaded in offline
  mode.

----------

- Uninstall recipes weren't loaded correctly in cases where
  no parts in the (new) configuration used the recipe egg.

---------------

- A new command-line argument, -U, suppresses reading user defaults.

- You can now suppress use of an installed-part database
  (e.g. .installed.cfg) by sprifying an empty value for the buildout
  installed option.

depended on were installed too.  This is nice under normal
circumstances, but when the install command is used with a list of
parts, then the promise is that *only* those parts will be installed.
This is an important use case, because it can speed development.

Use the logical size instead.

Both now must use the same name. Thus there is no need for a part 
'uninstall' option.

on windows.

Normalize extension names.

Remove a no-longer needed normaliation

Feature Changes
---------------

- Variable substitutions now reflect option data written by recipes.

- A part referenced by a part in a parts list is now added to the parts
  list before the referencing part.  This means that you can omit
  parts from the parts list if they are referenced by other parts.

- Added a develop function to the easy_install module to aid in
  creating develop eggs with custom build_ext options.

- The build and develop functions in the easy_install module now
  return the path of the egg or egg link created.

- Removed the limitation that parts named in the install command can
  only name configured parts.

- Removed support ConfigParser-style variable substitutions
  (e.g. %(foo)s). Only the string-template style of variable
  (e.g. ${section:option}) substitutions will be supported.
  Supporting both violates "there's only one way to do it".

- Deprecated the buildout-section extendedBy option.

----------

- We treat setuptools as a dependency of any distribution that
  (declares that it) uses namespace packages, whether it declares
  setuptools as a dependency or not.  This wasn't working for eggs
  intalled by virtue of being dependencies.

`67737 <https://launchpad.net/products/zc.buildout/+bug/67737>`_
     Verbose and quite output options caused errors when the 
     develop buildout option was used to create develop eggs.

`67871 <https://launchpad.net/products/zc.buildout/+bug/67871>`_
     Installation failed if the source was a (local) unzipped
     egg.

`67873 <https://launchpad.net/products/zc.buildout/+bug/67873>`_
     There was an error in producing an error message when part names
     passed to the install command weren't included in the
     configuration.

moved, rather than copied, removing them from the source directory.

buildout.

or setuptools, copy the develop eggs to the new buildout's
develop-eggs directory, rather than its eggs directory.

setuptools and zc.buildout.

Don't upgrade if the buildout command is non-local.