Recovered parser test whose content got broken in r12975, functionality broken in...

Recovered parser test whose content got broken in r12975, functionality broken in r14635.

Changed what used to be EXT_LINK_TEXT_CLASS to
define( 'EXT_LINK_TEXT_CLASS', '[^\]\\x00-\\x08\\x0a-\\x1F]' );
In plain English, do not allow control characters in description. We still allow tabs
there, since they may arrive from a paste.

We should probably make the space between the text and the description mandatory, it needs testing.

These tests only work with the Hash Preprocessor, since the DOM Preprocessor changes them into the
replacement character. Should we autolink an URL with a FFFD? That will require changing some regex
into unicode ones.