Add failing test for imported mixin with wrong path

When relative URLs are on, and there's an image referenced via url(...),
if the URL is unquoted, the generated CSS duplicates the base path
Experimental support for mixins with interpolated selectors.
 interpolated mixins, fixed: possible false match if variable contains `,`
Initial implementation of mixin guard `default` function (aka "mutually exclusive guards")
mixin guard `default`: `default` moved to functions.js + other minor improvements
Remove alpha from contrast calc, see #1724
Add link to docs project in contributing section
Add link to docs project

And add including solutions to bug reports
fix the benchmark less
update the changelog with details of the performance improvements
normalize the base path as well as the filename for sourcemaps. Fixes #1736
Merge branch 'master' of https://github.com/cloudhead/less.js
Merge branch 'unquoted-relative-url-in-mixin' of https://github.com/bdukes/less.js
Fix issue with urls in mixins
Merge pull request #1733 from Synchro/master

Remove alpha from contrast calc
Experimental support for "property name interpolation".
Experimental support for "property name interpolation", part-2.
Fix issue with unqouted urls in mixins having their context evaluated twice. Fix sourcemap test output
changelog
Merge branch 'master' of https://github.com/cloudhead/less.js