tell.py: Clarify on an ambiguous message, and remove a little bit of redundancy in a regular expression.

The message that was sent implied that the user would receive the message
  instantaniously, which is not the case, as they only get the message
  the moment they speak.

The regular expression matched A-Z when the string was lowercase.
Merge pull request #283 from Zarthus/tell-clarify

tell.py: Clarify on an ambiguous message, and remove a little bit of redundancy in a regular expression.