[Mediawiki-i18n] unified syntax in Messages.php ('foo' =>'...'versus 'bar' => "...")

[Platonides]

"..." syntax needs to escape more characters. "..." makes a processing into 
the text, so i think it worse. All the $1 parameters we use may need to be 
escaped to \$ to avoid php looking for a variable called $1 (or even give an 
error, as variable names need to start with a letter or underscore). $1 is 
not currently affected, but {$1} do need (think in templates).

And although writing wikitext can be horrible, it can also be difficult to 
write html into "..." (due to html params).