Fix wrong language comparison

If the applied element has no language attribute we use inherited
language value(present as this.language). But in this place we were
using elements lang attribute directly. Which can be undefined sometimes
and can cause expliticit fontfamily style added to child elements

Eg:
<html lang='en'>
..
<body>
<div lang='en'>

After applying FontA to body should be
<html lang='en'>
..
<body style="fontfamily='FontA, fallbacks';">
<div lang='en'>

but we were getting
<html lang='en'>
..
<body style="fontfamily='FontA, fallbacks';">
<div lang='en' style="fontfamily='FontA, fallbacks';>

That makes resetting not applying to child div since we never touch
child elements with explicit fontfamily value
Avoid duplicates in fontstack, reset only when fontfamily is null
Do not inherit fontfamily when language differs

If there is no explicit font for this language, it will
inherit the webfont for the parent.
But that is undesirable since language is different.
So inherit the original font of the element.
Define it explicitly so that inheritance is broken.
Merge pull request #31 from santhoshtr/bug49151

Do not inherit fontfamily when language differs