CSS: Support relative adjustment in any applicable unit

Fixes gh-1711
Closes gh-2011

(cherry picked from commit 9b03f6df88)

Conflicts:
	src/css.js
	src/effects.js

src/var/rcssNum.js

@@ -0,0 +1,7 @@
+define([
+	"../var/pnum"
+], function( pnum ) {
+
+return new RegExp( "^(?:([+-])=|)(" + pnum + ")([a-z%]*)$", "i" );
+
+});