pgsql: Make EXPLAIN sampling smarter, to avoid excessive sampling delay.

Log Message:
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Make EXPLAIN sampling smarter, to avoid excessive sampling delay.

Martijn van Oosterhout

Modified Files:
--------------
    pgsql/src/backend/commands:
        trigger.c (r1.201 -> r1.202)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c.diff?r1=1.201&r2=1.202)
    pgsql/src/backend/executor:
        execProcnode.c (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execProcnode.c.diff?r1=1.54&r2=1.55)
        instrument.c (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/instrument.c.diff?r1=1.14&r2=1.15)
        nodeBitmapAnd.c (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeBitmapAnd.c.diff?r1=1.7&r2=1.8)
        nodeBitmapIndexscan.c (r1.18 -> r1.19)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeBitmapIndexscan.c.diff?r1=1.18&r2=1.19)
        nodeBitmapOr.c (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeBitmapOr.c.diff?r1=1.6&r2=1.7)
        nodeHash.c (r1.102 -> r1.103)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeHash.c.diff?r1=1.102&r2=1.103)
    pgsql/src/include/executor:
        instrument.h (r1.13 -> r1.14)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/instrument.h.diff?r1=1.13&r2=1.14)