In haml command, when printing parse tree, only instantiate parser

Don't depend on creating an engine just to see the parse tree. This
makes it a bit easier to hack the compiler because you can still see a
parse tree even while you've temporarily broken the compiler during
work.

lib/haml/exec.rb

@@ -296,14 +296,16 @@ def process_result
 
         begin
 
-          engine = ::Haml::Engine.new(template, @options[:for_engine])
-          if @options[:check_syntax]
-            puts "Syntax OK"
+          if @options[:parse]
+            parser = ::Haml::Parser.new(template, ::Haml::Options.new(@options))
+            pp parser.parse
             return
           end
 
-          if @options[:parse]
-            pp engine.parser.root
+          engine = ::Haml::Engine.new(template, @options[:for_engine])
+
+          if @options[:check_syntax]
+            puts "Syntax OK"
             return
           end