bizgres - bizgres: Make the parsing of queue thresholds a little better

Log Message:
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Make the parsing of queue thresholds a little better - in the active case we
can now avoid float format, but unfortunately need to keep it for cost.
The reason being my lack of comfort in having a max cost threshold of 1e+19,
given we (or I anyway) don't seem to have any hard data about maximum statement
cost values for DSS systems.

Also fixed a bug where it was impossible to cancel a threshold from a queue
via alter, plus used the macro for 'invalid threshold' instead of a bare
number where I found it.

Modified Files:
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bizgres/postgresql/src/backend/commands:
queue.c (r1.1 -> r1.2)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/bizgres/bizgres/postgresql/src/backend/commands/queue.c.diff?r1=1.1&r2=1.2)
bizgres/postgresql/src/backend/parser:
gram.y (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/bizgres/bizgres/postgresql/src/backend/parser/gram.y.diff?r1=1.2&r2=1.3)
bizgres/postgresql/src/backend/utils/resscheduler:
README (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/bizgres/bizgres/postgresql/src/backend/utils/resscheduler/README.diff?r1=1.6&r2=1.7)