PHP error due to mime_content_type()

In asset.types.inc on line 283 of the -dev branch (I used 5--2, I assume that's where you're devving), there is an extra space in the function_exists() call to check for mime_content_type(). As a result, the if statement is firing back a false negative and mime_content_type() is being redeclared, which makes php quite unhappy. I guess this is only a problem for people with the Mimetype php extension in their php compilations (Maybe because mime_content_type() has been deprecated in favor of PECL? http://us2.php.net/manual/en/ref.mime-magic.php), but it fired back a very unhappy php error when I attempted to enable the module. This patch fixes the error.