Python versions prior to 2.6 have an issue clearing the environment variables
using ``os.environ.clear()`` (See http://bugs.python.org/issue3227).

Instead of modifying ``os.environ`` directly we use the ``subprocess``
module to run the commands in child processes which are given an explicit
environment which is a copy of the current ``os.environ`` augmented with
the per-part overrides.

See https://github.com/hexagonit/hexagonit.recipe.cmmi/issues/issue/1/#issue/1/comment/605362
for details.

Due to this change the hook scripts no longer have the augmented environment.
They can still access the buildout configuration to read the overrides but
need to do this manually.

See http://github.com/hexagonit/hexagonit.recipe.cmmi/issues#issue/1

After a failed attempt, if the user removes the __compile directory
but leaves the target directory untouched, and re-runs the buildout,
an OSError should not be raised.

When installation fails, the working directory is left in place: further
calls to cmmi recipe with the same arguments should not raise an
OSError.
Let the download recipe handle the error, and print a friendly error.

This change makes sure that the working directory is restored to the location
it was before running the recipe, regardless whether the execution of the
recipe is successful or not.

Thanks to Jonathan Ballet for pointing out this problem.

Replaced references to the ``download-directory`` option with the current spelling of ``download-cache``.

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@5527 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4584 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4582 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

1.0.1.


git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4539 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4537 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4536 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

build process. This adds significant control over the whole build process.


git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4535 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

source distributions.


git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4508 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d

git-svn-id: https://svn.hexagonit.fi/hexagonit.recipe.cmmi/trunk@4507 b96f28ea-bbdf-0310-b3b3-e15a02b9f88d