reworked guard comparison
Merge branch 'reworked-guard-comparison' of github.com:seven-phases-max/less.js into 2_0_0

Conflicts:
	lib/less/tree.js
	lib/less/tree/anonymous.js
	lib/less/tree/color.js
	lib/less/tree/condition.js
	lib/less/tree/dimension.js
	lib/less/tree/keyword.js
	lib/less/tree/quoted.js