jinja2_template imports zc.buildout, but uses zc.buildout.buildout (note
the double .buildout). As the result, when tried to use in standalone
mode, importing slapos.recipe.template.jinja2_template fails:

    In [1]: import slapos.recipe.template.jinja2_template
    ---------------------------------------------------------------------------
    AttributeError                            Traceback (most recent call last)
    Cell In[1], line 1
    ----> 1 import slapos.recipe.template.jinja2_template

    File ~/src/wendelin/slapos/slapos.recipe.template/slapos/recipe/template/jinja2_template.py:56
         53     raise AssertionError(*args)
         54 DEFAULT_CONTEXT['assert'] = _assert
    ---> 56 _buildout_safe_dumps = getattr(zc.buildout.buildout, 'dumps', None)
         57 DUMPS_KEY = 'dumps'
         58 DEFAULT_IMPORT_DELIMITER = '/'

    AttributeError: module 'zc.buildout' has no attribute 'buildout'

That happens because zc.buildout is just a package and does not import
anything from its submodules:

https://lab.nexedi.com/nexedi/slapos.buildout/blob/e9c39301/src/zc/buildout/__init__.py

So the correct way of importing is, thus, import `zc.buildout.buildout`.

-> Fix it.

The bug was there since 65cd02ec (Add jinja2-based template recipe
entry.)

/cc @vpelletier, @jerome

This extension is now builtin and no longer exist under the old name.
Since the test was just verifying that we can load extensions and uses
other extensions, we can just remove it from the test.

This fixes a regression in commit 0f8a8b27
("default: bring some of the jinja2 improvements by refactoring the 2 recipes").

Example:

foo.cfg:

  [foo]
  url = ...

bar.cfg:

  [buildout]
  extends = foo.cfg

  [foo]
  url =
  inline = blablah

Recipes must not distinguish the existence of an option from an empty
option value. It's a common mistake in recipes because that's natural
to do that in Python. However, buildout has no syntax to remove an
option when overriding a section.

This fixes commit 62f55c69
for Python 3.

- try to not rewrite on update if there's no change
- handle 'mode' the same way as in the jinja2 recipe

The expected usage of zc.buildout.download.Download() is that the caller is
supposed to remove the temporary files (cf [1] [2])

[1]: https://github.com/buildout/buildout/blob/3ed7c06bf7be594dcb3c906c2517ee438f059251/src/zc/buildout/download.txt#L55
[2]: https://github.com/buildout/buildout/blob/3da22a7dacb9a4d1f771e7763e014214c31d935b/src/zc/buildout/download.py#L171-L176

See merge request nexedi/slapos.recipe.template!5

setuptools 42.0.0 prints a warning:

   WARNING: The easy_install command is deprecated and will be removed in a future version

use a test normalizer to ignore this warning in doctest.

Local variable `template` is used for different things, it is bad. Use different variable name for different thing.

compile function takes a lot of time, thus this change saves time when the same source is used many times in apache frontend SR.