Added member to List.
Playing around with some mixin patterns.
Merge branch 'master' of https://github.com/brownplt/pyret-lang
check.arr
Merge branch 'master' into dep-mixins

Conflicts:
	src/lang/pyret-lib/experimental/check.arr
Java mixin initial attempt.
Added has-field to builtins.
Java extend and super in constructor.
Java method overriding with super.
Merge branch 'dep-mixins'
use Jonah's member