[Sass] Allow variables to be defined with :.

lib/sass/engine.rb

@@ -427,8 +427,8 @@ WARNING
       Script.var_warning(name, @line, line.offset + 1, @options[:filename]) if line.text[0] == ?!
 
       expr = parse_script(value, :offset => line.offset + line.text.index(value))
-      expr.context = :equals
-      Tree::VariableNode.new(name, expr, op == '||=')
+      expr.context = :equals if op =~ /=$/
+      Tree::VariableNode.new(name, expr, op =~ /^\|\|/)
     end
 
     def parse_comment(line)

lib/sass/script.rb

@@ -14,7 +14,7 @@ module Sass
   module Script
     # The regular expression used to parse variables.
     # @private
-    MATCH = /^[!\$](#{Sass::SCSS::RX::IDENT})\s*((?:\|\|)?=)\s*(.+)/
+    MATCH = /^[!\$](#{Sass::SCSS::RX::IDENT})\s*((?:\|\|)?[:=])\s*(.+)/
 
     # The regular expression used to validate variables without matching.
     # @private

lib/sass/tree/variable_node.rb

@@ -17,7 +17,7 @@ module Sass
       protected
 
       def to_src(tabs, opts, fmt)
-        "#{'  ' * tabs}$#{@name} #{'||' if @guarded}= #{@expr.to_sass}#{semi fmt}\n"
+        "#{'  ' * tabs}$#{@name} #{'||' if @guarded}: #{@expr.to_sass}#{semi fmt}\n"
       end
 
       # Loads the new variable value into the environment.