plpsm - plpgpsm: consistent handling exit and continue handlers in

Log Message:
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consistent handling exit and continue handlers in atomic block.

After catching exception I do rollback inner subtransaction -> needed for
correct excecution of any handler, and then I do rollback uter atomic
compound block, because I wont to correct execution all statements in
atomic coumpound statement.

Modified Files:
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    plpgpsm/src:
        pl_exec.c (r1.24 -> r1.25)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/plpsm/plpgpsm/src/pl_exec.c.diff?r1=1.24&r2=1.25)