Added guards checking to namespaces. Issue #1418.
Merge branch 'namespaces-guards-1418' of github.com:SomMeri/less-rhino.js into SomMeri-namespaces-guards-1418
Merge branch 'SomMeri-namespaces-guards-1418' into 2_0_0

Conflicts:
	lib/less/tree/mixin.js
	lib/less/tree/ruleset.js