verify the regex passed with the path-pattern option

Problem/Motivation

If you mess up the regex you get a lot of warnings on the command line but tome:static keeps on going. Instead it should stop:

      // Running the regex against an empty string should return 0 if the regex is valid, will return FALSE if there is an error.
      // Silence the warning since we're handling this ourselves.
      if (@preg_match($options['path-pattern'], '') === FALSE) {
        // I can't remember how we halt a Drush command with an error

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes