Be sure not to loose any var in case of multi macro inheritance

In case of multiple chained inheritance,with a bunch of big modules loading in combination with a local pillar, we had some weird jinja errors appearing complaining about salt not to be defined. Wheras it seems, it breaks. I think it may be caused by jinja loosing global vars in chain loaded templates.
If i am not wrong, this pull request fixes it, but i dont know how to make a simple reproducible test case

```
[TRACE   ] Added virt_query.output to output
local:
    Data failed to compile:
----------
    Rendering SLS "base:makina-states.controllers.mastersalt_master" failed: Jinja variable 'salt' is undefined
/var/cache/mastersalt/mastersalt-minion/files/base/makina-states/_macros/localsettings.jinja(11):
---
[...]
{%- import "makina-states/_macros/funcs.jinja" as funcs with context %}
{#- expose imported macros #}
{%- set funcs = funcs %}

{#- see _modules/mc_localsettings.py for exposed settings #}
{%- set settings = salt['mc_localsettings.settings']() %}    <======================
{%- set metadata = salt['mc_localsettings.metadata']() %}
{%- set registry = salt['mc_localsettings.registry']() %}


{# pythonSettings #}
[...]
---