Use Drupal standard error logging instead of error_log

The "error_log" function is not a standard way to do logging in Drupal which means that these logs will not be picked up in typical reports.

This patch makes a beginning of the work to turn it into a proper watchdog message, but there is still work necessary to properly use the internationalization tools of watchdog.

I needed to do this just to reduce the noise that I got while running "drush cron" on my tattlerapp site.