Bug-report follow-up

[Michael Carmack]

Ok, it appears someone has put an absolute path to a header file in
the 'configure.in' script. This occurs on line 275. On systems that 
don't store unistd.h under /usr/include the test program will fail and 
cause configure to assume the usleep return type is 'int'. This breaks
the compile later on for systems that return void (shown in the logs
attached to the previous email).

m.