the current way of passing '-DBIG_TABLES' to the compilers.

This is needed even in 4.0, as 'Do-compile-all' must use this new approach for
all "max" builds in 4.0, 4.1, and up.


acinclude.m4:
  Provide a new macro 'MYSQL_CHECK_BIG_TABLES' to check a '-with-big-tables' option 
  and set the CPP symbol 'BIG_TABLES' accordingly.
configure.in:
  Call the new 'MYSQL_CHECK_BIG_TABLES' macro.