Don't insist on pg_dumpall and psql being present in the old cluster,
since they are not needed. Do insist on pg_resetxlog being present
(in both old and new), since we need it. Also check for pg_config,
but only in the new cluster. Remove the useless attempt to call
pg_config in the old cluster; we don't need to know the old value of
--pkglibdir. (In the case of a stripped-down migration installation
there might be nothing there to look at anyway, so any future change
that might reintroduce that need would have to be considered carefully.)
Per my attempts to build a minimal previous-version installation to support
pg_upgrade.
1. Don't reimplement S_ISDIR() and S_ISREG() badly.
2. Don't reimplement access() badly.
This code appears to have been copied from ancient versions of the
corresponding backend routines, and not patched to incorporate subsequent
fixes (see my commits of 2008-03-31 and 2010-01-14 respectively).
It might be a good idea to change it to just *call* those routines,
but for now I'll just transpose these fixes over.
* There is no chmod() on Windows.
* Must always use the 3-parameter version of open()
* There is no dynloader.h - but it also appears unnecessary on all platforms
* Don't include shlobj.h because it causes compile errors, and from what I can
see it's not actually used. This may need to be added back for mingw
and/or cygwin in the worst case.
