To be used for zope's inituser file, for example.

UTF-8 encoding for template imports was hardcoded from the beginning -
from 320f29b2 (Add jinja2 "import" directive support.)

Since in the previous patch we added option for input/output encoding,
it makes sense to also use it, instead of hardcoding utf-8.

/reviewed-by @vpelletier  (on nexedi/slapos.recipe.template!1)

Currently slapos.recipe.template:jinja2 fails if source contains
non-ascii input:

    <BLANKLINE>
    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    Traceback (most recent call last):
      File ".../site-packages/zc/buildout/buildout.py", line 1992, in main
        getattr(buildout, command)(args)
      File ".../site-packages/zc/buildout/buildout.py", line 550, in install
        [self[part]['recipe'] for part in install_parts]
      File ".../site-packages/zc/buildout/buildout.py", line 1135, in __getitem__
        options._initialize()
      File ".../site-packages/zc/buildout/buildout.py", line 1239, in _initialize
        self.initialize()
      File ".../site-packages/zc/buildout/buildout.py", line 1248, in initialize
        self.recipe = recipe_class(buildout, name, self)
      File ".../slapos.recipe.template/slapos/recipe/template/jinja2_template.py", line 208, in __init__
        env.compile(source, filename=template),
      File ".../site-packages/jinja2/environment.py", line 551, in compile
        source = self._parse(source, name, filename)
      File ".../site-packages/jinja2/environment.py", line 470, in _parse
        return Parser(self, source, name, encode_filename(filename)).parse()
      File ".../site-packages/jinja2/parser.py", line 31, in __init__
        self.stream = environment._tokenize(source, name, filename, state)
      File ".../site-packages/jinja2/environment.py", line 501, in _tokenize
        source = self.preprocess(source, name, filename)
      File ".../site-packages/jinja2/environment.py", line 495, in preprocess
        self.iter_extensions(), text_type(source))
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xd0 in position 219: ordinal not in range(128)

it also fails writing-out non-ascii input (which could originate even
programmatically even if source was purely ascii):

    <BLANKLINE>
    An internal error occurred due to a bug in either zc.buildout or in a
    recipe being used:
    Traceback (most recent call last):
      File ".../site-packages/zc/buildout/buildout.py", line 1992, in main
        getattr(buildout, command)(args)
      File ".../site-packages/zc/buildout/buildout.py", line 666, in install
        installed_files = self[part]._call(recipe.install)
      File ".../site-packages/zc/buildout/buildout.py", line 1407, in _call
        return f()
      File ".../slapos/slapos.recipe.template/slapos/recipe/template/jinja2_template.py", line 227, in install
        out.write(self.template.render(**self.context))
    UnicodeEncodeError: 'ascii' codec can't encode characters in position 206-211: ordinal not in range(128)

Fix it.

@vpelletier suggested to add `encoding` option so it is flexible and
'utf-8' is not hardcoded.

/reviewed-by @vpelletier  (on nexedi/slapos.recipe.template!1)

Although very unlikely here, it's good pratice to write code without possible
race conditions. The only remaining one here is when anouther process create
a file (with the same output path) between its deletion and its creation.

They should not be needed when buildout handles its own serialisation.

Based largely on work by Timothée Lacroix <timothee.lacroix@tiolive.com>,
plus:
- reworked loader classes
- reduced unnecessary diffs
- added rawfile and rawfolder types
- documented & tested

umask cannot set a regular file as executable, nor allows setting
suid/sgid/sticky bits.
Using chmod properly, there is no security problem.

Useful when extending another section from same file.

This test case was accidentally reusing a previous template.

Noticed by Timothée Lacroix <timothee.lacroix@tiolive.com>

Patch by Timothée Lacroix <timothee.lacroix@tiolive.com>

Patch by Timothée Lacroix <timothee.lacroix@tiolive.com>

Reported by Timothee Lacroix.

Loads support should not be required: the use-case is writing python values
when generating a buildout.cfg file.

Test the latter, and document how to work around the former.

Also, fix pyc files gitignore globing.

Buildout way couldn't install some (dependency) eggs for an unknown reason
(zope.exception on some python environments, Jinja2 needed by a future
extension...) and "setup.py test" just works, with fewer lines at this.
Also, drop zope.testing dependency altogether:
- zope.testing.doctest is deprecated
- zope.testing.renormalizing is not really needed for this test