Ignore indentation inside multiline comments

Fixes #464

CHANGELOG.md

@@ -45,6 +45,9 @@
   Internet Explorer earlier than version 9.
   (thanks [Doug Mayer](https://github.com/doxavore))
 
+* Fix multiline silent comments: Haml previously did not allow free indentation
+  inside multline silent comments.
+
 ## 3.1.5 (Unreleased)
 
 * Respect Rails' `html_safe` flag when escaping attribute values

REFERENCE.md

@@ -942,6 +942,7 @@ For example:
     -#
       This won't be displayed
         Nor will this
+                       Nor will this.
     %p bar
 
 is compiled to:

lib/haml/parser.rb

@@ -151,7 +151,7 @@ END
           @parent = @parent.children.last
         end
 
-        if !flat? && @next_line.tabs - @line.tabs > 1
+        if !@haml_comment && !flat? && @next_line.tabs - @line.tabs > 1
           raise SyntaxError.new("The line was indented #{@next_line.tabs - @line.tabs} levels deeper than the previous line.", @next_line.index)
         end
 

test/haml-spec

@@ -1 +1 @@
-Subproject commit e0c6969fc1e054c8e6a91bc8edee319e4001064f
+Subproject commit 4164a878f6a4cec98d538ecc5ef6be3dbf34050e