balanceTags doesn't understand namespaced tags

[Otto42]

Try to put something like this into a post (with unfiltered_html enabled):

<test:something>
garbage
</test:something>

If the balance tags option is enabled, it will mangle this content into this:

<test :something>
garbage
</test>

Reason: Balance tags doesn't understand that colons can be part of tag names.

This makes using things like XFBML (part of Facebook Connect) in posts very difficult.

[dd32]

(In [13913]) Recognise namespaces in tags for balanceTags(). Fixes #11968