Fix #861 and introduce tests for errors

lib/less/parser.js

@@ -780,6 +780,8 @@ less.Parser = function Parser(env) {
                     var elements = [], e, c, args = [], arg, index = i, s = input.charAt(i), name, value, important = false;
 
                     if (s !== '.' && s !== '#') { return }
+                    
+                    save(); // stop us absorbing part of an invalid selector
 
                     while (e = $(/^[#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/)) {
                         elements.push(new(tree.Element)(c, e, i));
@@ -818,6 +820,8 @@ less.Parser = function Parser(env) {
                     if (elements.length > 0 && ($(';') || peek('}'))) {
                         return new(tree.mixin.Call)(elements, args, index, env.filename, important);
                     }
+                    
+                    restore();
                 },
 
                 //