Attached patch gets rid of most of the remaining warnings on a VC++
build. Summary is:
* A bunch of places that had different const specifyer in the header and
in the body of the function. (contrib/intarray, src/timezone)
* 1.2 and such constants are double and cause warning. Define as floats
(contrib/pg_trgm and contrib/tsearch2)
* HAVE_STRERROR is defined by python, so only conditionally redefine it
in pg_config.h
* NULL function pointer in SSL call cast to the correct pointer type
* ssize_t is defined in pg_config_os.h, remove from libpq-int.h
* Always skip warning 4102 ("label nnn: unreferenced label") caused by
bison.
* Support for ignoring linker warnings, and ignore the warning about
PRIVATE on DllRegisterServer. Can't fix properly because PRIVATE is
not supported by mingw.
