strip schema name from ADD CONSTRAINT / CREATE INDEX

 * Pg tablenames may have a schema prefix.  This leads to invalid ADD
   CONSTRAINT / CREATE INDEX statments being generated by ->deploy(),
   since constraint and index names may not have a period in them.  This
   patch strips the schema part from the table name when constructing
   unique index and constraint names.  The fix was taken from
   ribasushi's email to the mailing list:

   http://lists.scsys.co.uk/pipermail/dbix-class/2013-February/011141.html