Re: allow benign typedef redefinitions (C11)

Hello,

Here's another simple piece that I noticed while fooling around with the doxygen report -- genam.h was including tidbitmap.h and relcache.h for the sake of one typedefs each, and this was bleeding in other places in a rather random fashion, particularly through amapi.h. I propose the following to fix it. The changes to inet.h and varbit.h are surprising, but required. (It's possible that we should be including varatt.h in more datatype headers than just those two, but at least these are the ones that complained. So another option would be to include varatt.h in the files that include those headers. However, that seems to me to be the wrong direction).

--
Álvaro Herrera