Move error reporting to dedicated subroutine

We use say here and there when reporting errors. Centralize all error
reporting to one subroutine where it can easily be streamlined.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Handle repository errors with a common subroutine

We prefix all errors related to a specific repository with the prefix of
the user name and repository name. Handle this through a subroutine that
passes the message to the global error routine.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>