Refactor configure.ac to move INCLUDE_INTERFACE logic to Autoconf

[GreyStinger]

Reworked the configure scripts to not link ncurses if the other checks fail, and ensure we don't try and build with the interactive interface if we don't have ncurses.

[GreyStinger]

So commit 9608adc is purely aesthetic. I decided to put it up anyway as LP64 systems should all have 4byte unsigned ints.
The only time this would change anything would be the seemingly unlikely scenario where both int and long were 4 bytes, where now int would be favored instead of long?

[infrastation]

Re IRIX and BSDi detection in Autoconf, the host_os variable is readily available for that, there is no need to compile and run a program. On a more generic note, these OSes are extinct so that part of the solution space is moot and can be lost. Then the check for ncurses library could be hinged on the presence of ncurses header and shmget() (to solve the original problem of linking with ncurses when the interface is disabled) and the resulting code would be easier to follow. That's how much I can tell from the code. For posterity, shared memory is not available on Haiku.

[GreyStinger]

Right, I was worried about the IRIX and BSDi part as I was not able to test what the canonical host-system types would be. I'll post a fix removing those compiles and checks.