Add new parameter --tiles that accept only uniform split. I considered
supporting the syntax of --tiles-width-split for this, but writing
--tiles=u2xu2 is just not as intuitive as --tiles=2x2, and there is
hardly ever any reason to use anything but uniform split. The more
cumbersome --tiles-width-split and --tiles-height-split parameters
are still there to allow finer control.
Prevents a conflict with config.h and src/config.h so that the config.h
generated by configure is included in global.h. Fixes problems with
large input files on 32-bit systems.