pg_upgrade's exec_prog() coding improvement

Hi,

I've been bitten twice by exec_prog()s API, so here's a patch to try to
make it a bit harder to misuse.

There are two main changes here; one is to put the logfile option as the
first argument; then comes a bool, then the format string.  This means
you get a warning if you pass the wrong number of arguments before the
format; previously I mis-merged in the KEY SHARE patch so that I was
passing the log file as format, and the compiler didn't complain at all.

The other interesting change I did was move the responsibility of adding
SYSTEMQUOTE and the ">> %s 2>&1" redirections to exec_prog itself,
reducing clutter in the caller.  This makes the callers a lot easier to
read.

One other minor change I did was split it in two versions: a simpler one
with less frammishes, that doesn't let you supply an alternative log
file and doesn't return a status value.  This is used for all but one of
the callers; only that one caller was interested in the result value
anyway.  And that caller is also the only one that passes an
opt_log_file other than NULL, so I removed that from the simple version.

Lastly, I removed the is_priv boolean, which seems pretty pointless;
just made all calls set the umask inconditionally.  The only caller
doing this was the cp/xcopy call, and I don't see any reason for this to
be different from other callers.

This makes pg_upgrade a bit more readable.

If anyone can test this on Windows I would be appreciate it.

One problem with this is that I get this warning:

/pgsql/source/HEAD/contrib/pg_upgrade/exec.c: In function ‘s_exec_prog’:
/pgsql/source/HEAD/contrib/pg_upgrade/exec.c:96:2: warning: function might be possible candidate for ‘gnu_printf’
formatattribute [-Wmissing-format-attribute] 
/pgsql/source/HEAD/contrib/pg_upgrade/exec.c:96:2: warning: function might be possible candidate for ‘gnu_printf’
formatattribute [-Wmissing-format-attribute] 

I have no idea how to silence that.  Ideas?

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services