Add cucumber scenarios for markdown pages with erb layout

These are tests for middleman/middleman#860.
Set current_engine on the context, not self, since we dup self and use that for each render loop. Closes #860
Apparently Ruby 1.8 doesn't have Proc.source_location
And by 1.8, I mean MRI 1.8
dont bother with jruby 1.8 mode
Implement generic  which is a simple way to build a file from Rack
new rc
dum dum dum.....
Prevent relative asset helper from munging data URIs. Closes #938.
Check if set is redefining a param at the class level. Fixes #939
bump ver
Fix content_tag helper, only try to mark content as safe if it is not a hash of options
Merge pull request #941 from krautcomputing/fix_content_tag_helper

Fix content_tag helper, only try to mark content as safe if it is not a hash of options
tests for content_tag escaping
bump listen
implement redirect support
Update gitignore
Merge pull request #943 from southpolesteve/patch-1

Add .DS_Store to generated .gitignore
dont hardcode ignored build dir name
fix layouts with implied extensions