OMP::User: add option to return extracted email

OMP::User::extract_user_from_email now takes an additional parameter
which can be a scalar reference to which the extracted email address
should be written.  This is because extracting the email address
is a useful feature of this routine even if it then goes on to
fail to construct an OMP::User object.
mail2feed: search by email address first

When trying to identify the author of an email (as an OMP
user), now search first by the email address.  See fault
20140717.002 for more information.  Also include a version
number in the log so that the version of this script
can be identified.