offapi again builds faster; user of gb_Deliver_deliver responsible for the directory

[Tor Lillqvist]

> So, maybe next improvement would be to call cp once for all files from
> the same directory.

As we de facto are requiring to use our own fork of Make anyway
(aren't we?), couldn't we add "touch", "mkdir" and "cp" functions to
Make? Implementing those should be fairly trivial.

If we don't want to require our own Make fork, we could wrap these in
gbuild macros that check the Make version and call external commands
instead if needed.

While at it, we could then add a"ifeq" and "ifneq" functions (don't
confuse with the line-based "ifeq" and "ifneq" directives processed
while reading in makefiles). That would enable making many of the
conditionals easier to understand, I think. Such macros would be
harder to wrap portably, though, I think.

--tml