newline in executable= causes assert failure on exec

Taking advantage of buildout's ability to transparently break attribute values across line causes newline characters to get stuck in them that later cause problems.

Example:

    executable =
        ${buildout:parts-directory}/python243/bin/python

results in the string:

    executable='\n/home/jeff/Clients/ZeOmega/task-CacheBySize/parts/python243/bin/python'

which causes use of this path in invoking setup.py within a recipe to fail:

An internal error occured due to a bug in either zc.buildout or in a
recipe being used:
Traceback (most recent call last):
  File "/home/jeff/Clients/ZeOmega/task-CacheBySize/lib/python2.5/site-packages/zc.buildout-1.2.1-py2.5.egg/zc/buildout/buildout.py", line 1509, in main
    getattr(buildout, command)(args)
  File "/home/jeff/Clients/ZeOmega/task-CacheBySize/lib/python2.5/site-packages/zc.buildout-1.2.1-py2.5.egg/zc/buildout/buildout.py", line 473, in install
    installed_files = self[part]._call(recipe.install)
  File "/home/jeff/Clients/ZeOmega/task-CacheBySize/lib/python2.5/site-packages/zc.buildout-1.2.1-py2.5.egg/zc/buildout/buildout.py", line 1091, in _call
    return f()
  File "/var/tmp/buildout/eggs/plone.recipe.zope2install-3.0-py2.5.egg/plone/recipe/zope2install/__init__.py", line 227, in install
    ) == 0
AssertionError

Solution:

  Append a call to .strip() in two places in zc/recipe/egg/egg.py and zc/recipe/egg/custom.py:

      options['executable'] = buildout[python]['executable'].strip()

  This approach keeps any whitespace -within- the name, as might be desired in some cases.