Re: define bool in pgtypeslib_extern.h

I wrote:
> I'm inclined to think that we need to make ecpglib.h's bool-related
> definitions exactly match c.h, which will mean that it has to pull in
> <stdbool.h> on most platforms, which will mean adding a control symbol
> for that to ecpg_config.h. I do not think we should export
> HAVE_STDBOOL_H and SIZEOF_BOOL there though; probably better to have
> configure make the choice and export something named like PG_USE_STDBOOL.

Here's a proposed patch that does it like that.

I'm of two minds about whether to back-patch or not. This shouldn't
really change anything except on platforms where sizeof(_Bool) isn't
one. We have some reason to think that nobody is actually using
ecpg on such platforms :-(, because if they were, they'd likely have
complained about breakage. So maybe we should just put this in HEAD
and be done.

regards, tom lane