previously had a number of flaws, perhaps most notably when an application
fired up N transfers at once as then they wouldn't pipeline at all that
nicely as anyone would think... Test case 530 was also updated to take the
improved functionality into account.

while () => while()
and some other minor re-indentings

cache within the multi handle.

linked list for name resolved data, even on hosts/systems with only IPv4
stacks as this simplifies a lot of code.

memory.h is included everywhere for this.

not used by any code in libcurl!

more in the same style as other curl source code. The only actual code change
is an added check after a malloc() call.

used for "exported" globals.

Reminder for the future: when we're using malloc() we MUST include <stdlib.h>
as otherwise 64bit archs go bananas.

Bug report #517687