convert_smilies optimization

[Nazgul]

Now that smilies are built using a regex, it is possible for us to optimize convert_smilies.

It splits and loops through all content passed to it, calling a regex on each line.
The attached patch replaces that loop with a single regex.

Present patch also fixes #3216.

(In [4360]) Smilies optimization from Nazgul. fixes #3201 #3216