pgsql: Two fixes from Tom Lan.

Log Message:
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Two fixes from Tom Lan. See the posting "[PATCHES] A couple of
proposed pgbench changes" on 2005/11/29 for more details.

The change at line 490 updates doCustom's local variable "commands"
after selecting a new file (command sequence).  I think that the
existing coding will cause the thing to use the first command of the
old sequence in the remainder of the routine, which would be a bug.
I have not tried to set up a test case to prove it, though.

The other two changes cause doCustom to loop after processing a
meta-command.  This might be a bit controversial, but as the code
is currently written, each meta-command "costs" one cycle of the
outer select() loop.  Thus, for example, with the default TPC-B script,
once a backend returns "COMMIT" it will not receive a new command
until four cycles of issuing commands to other backends have elapsed.
(You can see this very easily by strace'ing pgbench under load.)

Tags:
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REL8_1_STABLE

Modified Files:
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    pgsql/contrib/pgbench:
        pgbench.c (r1.45.2.2 -> r1.45.2.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/pgbench.c.diff?r1=1.45.2.2&r2=1.45.2.3)