Amend language variable support

lib/ace/mode/sh_highlight_rules.js

@@ -58,11 +58,6 @@ var ShHighlightRules = function() {
          ).split('|')
     );
 
-    var builtinVariables = lang.arrayToMap(
-            // TODO
-        ('$?|$$|$!|$SHLVL').split('|')
-    );
-
     var integer = "(?:(?:[1-9]\\d*)|(?:0))";
     // var integer = "(?:" + decimalInteger + ")";
 
@@ -74,9 +69,10 @@ var ShHighlightRules = function() {
     var fileDescriptor = "(?:&" + intPart + ")";
 
     var variableName = "[a-zA-Z][a-zA-Z0-9_]*";
-
     var variable = "(?:(?:\\$" + variableName + ")|(?:" + variableName + "=))";
 
+    var builtinVariable = "(?:\\$(?:SHLVL|\\$|\\!|\\?))";
+
     this.$rules = {
         "start" : [ {
             token : "comment",
@@ -84,6 +80,9 @@ var ShHighlightRules = function() {
         }, {
             token : "string",           // " string
             regex : '"(?:[^\\\\]|\\\\.)*?"'
+        }, {
+            token : "variable.language",
+            regex : builtinVariable
         }, {
             token : "variable",
             regex : variable
@@ -105,8 +104,6 @@ var ShHighlightRules = function() {
                     return "keyword";
                 else if (languageConstructs.hasOwnProperty(value))
                     return "constant.language";
-                else if (builtinVariables.hasOwnProperty(value))
-                    return "support.function";
                 else if (value == "debugger")
                     return "invalid.deprecated";
                 else