Changes for removing libcurl.def file on Win32.
Mark public functions with "CURL_EXTERN".

curl/multi.h header to work better in winsock-using apps.

known to really NEED it as another system that doesn't have it came up:
very old Linux libc5-based systems (as addition to all HPUX versions).

The only known system at this point is AIX.

make an adjustment to catch this.

AIX when this fix is applied and I cannot see how this will break any
systems.

include sys/time.h as well