Use "preg" instead of "ereg"

PHP offers two different function groups for regular expressions. The ereg functions expect a POSIX-style pattern syntax, while preg functions use a perl-compatible syntax.

Not only does Drupal mostly use the latter, php.net actually states that the latter is faster and it seems that ereg may be removed entirely in PHP 6. However, six places remain where core uses ereg. I don't see any problem with rewriting these expressions for preg instead, which would standardize core on a single form and may (negligibly) improve performance.

If there is a problem or a disadvantage with using preg in these places, this should probably be documented inline (currently isn't).

Here's a grep.

$ grep ereg -R includes/ modules/
includes/file.inc:    $regex = '/\.(' . ereg_replace(' +', '|', preg_quote($extensions)) . ')$/i';
includes/file.inc:        elseif ($depth >= $min_depth && ereg($mask, $file)) {
includes/unicode.inc:  if (!$bom && ereg('^<\?xml[^>]+encoding="([^"]+)"', $data, $match)) {
includes/unicode.inc:      $data = ereg_replace('^(<\?xml[^>]+encoding)="([^"]+)"', '\\1="utf-8"', $out);
modules/blogapi/blogapi.module:  if (eregi('<title>([^<]*)</title>', $contents, $title)) {
modules/blogapi/blogapi.module:    $contents = ereg_replace('<title>[^<]*</title>', '', $contents);