add ability to set cache_location for compass via configuration
feature #270 add ability to set cache_location for compass via configuration (robertfausk)

This PR was squashed before being merged into the 2.4-dev branch (closes #270).

Discussion
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add ability to set cache_location for compass via configuration

Also see kriswallsmith/assetic/issues/268

How to use it:
```
# app/config/config.yml
...
# assetic configuration
assetic:
    filters:
        compass:
            cache_location: %kernel.cache_dir%
...
```

Commits
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363bbef add ability to set cache_location for compass via configuration