patch: Review handling of MOVE and FETCH (ToDo)

Hello,

this small patch complete MOVE support in plpgsql and equalize plpgsql
syntax with sql syntax.

There are possible new directions:

FORWARD expr, FORWARD ALL, BACKWARD expr, BACKWARD all.

These directions are not allowed for FETCH statement, because returns more rows.

This patch is related to ToDo issue: Review handling of MOVE and FETCH

Regards
Pavel Stehule

p.s. Scrollable cursors are supported yet in plpgsql. Do you know,
somebody, why this point is in ToDo (plpgsql) still?