pg_ctl - tighten command parameter checking

The attached patch improves the command parameter checking of pg_ctl.

At present, there is nothing to check that the parameter given with a
parameter-taking option is actually valid. For example, -l can be given
without a following logfile name; on a strict POSIX shell such as ash,
you will get a subsequent failure because of too many shifts, but bash
will let it pass without showing any error. The patch checks that each
parameter is not empty and is not another option.

A consequence of this change is that no command-line parameter can begin
with "-" (except for the parameter to -o); this seems a reasonable
restriction.

For consistency and clarity, I have also changed every occurrence of
"shift ... var=$1" to "var=$2 ... shift".

--
Oliver Elphick Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight http://www.lfix.co.uk/oliver
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