Rename Limit in RT::Tickets to LimitField, so ->Limit acts as elsewhere

The old-style LimitFoo methods now call LimitField, which goes through
the Restrctions and Clauses machinery.  For compatibility with the rest
of SearchBuilder, however, it is exceedingly useful to have ->Limit act
immediately.
(cherry picked from rt commit 9e7da014a8150e1e781a3b18dd69d779e27580aa)
Use new Limit Functions
fix erroneous replace
System instance is 1
More role changess