* Add failing scenario with examples of partial locals usage
```cucumber
Scenario: Partials can be passed locals # features/partials.feature:37
Given the Server is running at "partials-app" # lib/middleman-core/step_definitions/server_steps.rb:65
When I go to "/locals.html" # lib/middleman-core/step_definitions/server_steps.rb:74
Then I should see "Local vars are 'foo', 'bar' and 'baz'" # lib/middleman-core/step_definitions/server_steps.rb:90
expected "Local vars are '', '' and 'baz'\n\n" to include "Local vars are 'foo', 'bar' and 'baz'"
Diff:
@@ -1,2 +1,2 @@
-Local vars are 'foo', 'bar' and 'baz'
+Local vars are '', '' and 'baz'
(RSpec::Expectations::ExpectationNotMetError)
./lib/middleman-core/step_definitions/server_steps.rb:91:in `/^I should see "([^\"]*)"$/'
features/partials.feature:40:in `Then I should see "Local vars are 'foo', 'bar' and 'baz'"'
```
* Use EnhancedHash when initializing hash in partial helper
To allow keys to be fetched either from symbols or strings, as before
v4.1.0.
