Replace deprecated ereg_* functions with equivalent preg_*

Anyone available to review this. Especially check that the log_messages changes work properly.

This patch seems to work for me

Definitely an improvement, but now I get a warning in place of the error:

preg_match(): Delimiter must not be alphanumeric or backslash in     [warning]
/usr/local/drush/includes/command.inc on line 521.

It seems to be unhappy with line 423 of the same file:
$files = drush_scan_directory($path, '\.drush\.inc$');

can someone comment on this error report?

convert that to

$files = drush_scan_directory($path, '/\.drush\.inc$/');

can anyone confirm?

droplet seems to have fixed the problem I was having. I didn't run a full test, but all of the tasks I usually run work as I expect them to.

committed. thanks.