- remove elf_caddr_t. It's positively dangerous to #define this since
   elf_caddr_t foo, bar; creates variables of different types (foo is
   char *, bar is char).
 - rewrite large chunks of create_elf_tables(), it needed cleaning anyway.
 - add upwards-growing stack support to create_elf_tables.
 - redefine the ARCH_DLINFO stuff on powerpc -- it's tested, works.
 - add upwards-growing-stack support to exec.c too.