The Bluesmobile

Fixes

• Fix segfault when comparing pseudo selectors (@xzyfer, #2289)
• Fix thread-safety for mixin recursions check (@mgreter, #2286)
• Fix false parser errors (@xzyfer, #2095)
• Fix bad source mappings for interpolated selectors (@mgreter, #2224)
• Fix not erring when encountering bad interpolations (@mgreter, #2081)
• Fix some error messages to match Ruby Sass (@mgreter, #2267)