* vax-tdep.c: Tweak comments. Reorder include files. Don't

* vax-tdep.c: Tweak comments.  Reorder include files.  Don't
include "symtab.h", "opcode/vax.h" and "inferior.h".
(vax_skip_prologue): Replace calls to read_memory_integer by calls
to read_memory_unsigned_integer.
(vax_gdbarch_init): Reorder.
(_initialize_vax_tdep): Spell out prototype.
* Makefile.in (vax-tdep.o): Update dependencies.