Improved handling of regex. (issue #309)

- Added proper handling of regex substitution expressions in the
  'report' command
- Substitions that don't change the original question are now ignored and
  an error reply message is given
- Forced addition of trailing space when using '^' pattern since
  leading/trailing whitespace is stripped by the bot
Minor fix for 'showreport' command.

- Bug introduced in b5501e5.
Updated messages for editing errors.

- Added error message for 'edit' command when the edit is the same as the
  old question
- Updated regex error message when expression results in no change