Add support for pre-wrap and pre-line values for white-space.

This is mostly straightforward.  I had to modify a couple of places
which were accidentally discarding whitespace.

Fixes #1513.

components/gfx/text/util.rs

@@ -38,7 +38,7 @@ pub fn transform_text(text: &str,
                     output_text.push(ch);
                 }
             }
-            text.len() > 0 && is_in_whitespace(text.char_at_reverse(0), mode)
+            false
         },
 
         CompressionMode::CompressWhitespace | CompressionMode::CompressWhitespaceNewline => {