[Patch] MacOS X support

First of all, thanks for making libtai available! I've attached a  
patch that makes libtai compile without warning on MacOS 10.4. Most  
of it is cosmetic, but the additional include files are required for  
leapsecs_read.c because the implicit declaration of read() has it  
returning an int when in fact it returns ssize_t (a long int). This  
causes libtai to believe the read() returned 0 (because it is only  
examining the upper 4 bytes of the returned number). libtai then  
reports itself unable to read the leap seconds file and dies.

	Cheers,
	David