highlight: fix page layout with empty first and last lines

Repeated newlines were stripped by pygmentize, now give the option not to do so.

hgext/highlight/highlight.py

@@ -38,12 +38,13 b' def pygmentize(field, fctx, style, tmpl)'
 
     # To get multi-line strings right, we can't format line-by-line
     try:
-        lexer = guess_lexer_for_filename(fctx.path(), text[:1024])
+        lexer = guess_lexer_for_filename(fctx.path(), text[:1024],
+                                         stripnl=False)
     except (ClassNotFound, ValueError):
         try:
-            lexer = guess_lexer(text[:1024])
+            lexer = guess_lexer(text[:1024], stripnl=False)
         except (ClassNotFound, ValueError):
-            lexer = TextLexer()
+            lexer = TextLexer(stripnl=False)
 
     formatter = HtmlFormatter(style=style)