gethostbyname_r arg-number checks no longer made if there isn't any
gethostbyname_r function!
aborts the configure if socket() is absent

curl issues when doing a regular HTTP post. This should not be taken light-
heartedly though. Replacing them might get you into trouble!

the AIX-styles as well.
I added --disable-thread to allow a user to disable all testing for
thread-safe functions being present and thus go with the good old style
functions. This might become handy if (when?) I add a bug in the threaded
code, like the AIX code I have now but can't test!

the AIX-style as well. The AIX-stuff is *NOT* verified to work.