Unhelpful error if an executable cannot be run

[Thomas Lotze]

If the Python executable to be used for a part cannot be run (perhaps because its path has a typo or whatever), the attempt to find out its version number takes the OS's error message for the command output and raises an exception when trying to interpret the string as "Python x.y.z":

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/thomas/OSS/zc.buildout/src/zc/buildout/buildout.py", line 1659, in main
    getattr(buildout, command)(args)
  File "/home/thomas/OSS/zc.buildout/src/zc/buildout/buildout.py", line 532, in install
    installed_files = self[part]._call(recipe.install)
  File "/home/thomas/OSS/zc.buildout/src/zc/buildout/buildout.py", line 1203, in _call
    return f()
  File "/var/lib/python-eggs/zc.recipe.testrunner-1.2.0-py2.4.egg/zc/recipe/testrunner/__init__.py", line 43, in install
    eggs, ws = self.egg.working_set(('zope.testing', ))
  File "/var/lib/python-eggs/zc.recipe.egg-1.2.2-py2.4.egg/zc/recipe/egg/egg.py", line 89, in working_set
    allow_hosts=self.allow_hosts,
  File "/home/thomas/OSS/zc.buildout/src/zc/buildout/easy_install.py", line 799, in install
    allow_hosts=allow_hosts)
  File "/home/thomas/OSS/zc.buildout/src/zc/buildout/easy_install.py", line 192, in __init__
    python=_get_version(executable))
  File "/home/thomas/OSS/zc.buildout/src/zc/buildout/easy_install.py", line 90, in _get_version
    pystring, version = version.split()
ValueError: too many values to unpack

The error message should say that the executable cannot be run, and display the path used in the attempt.