Improve header information displayed with objdump -P for PE binaries.

  * od-pe.c (targ_info): New array.
  (get_target_specific_info): New function.
  (decode_machine_number): Retire.  Use get_target_specific_info instead.
  (is_pe_object_magic): Likewise.
  (dump_pe_file_header): Display more information.
  Rework layout to be similar to that from 'objdump -p'.
  Add code to handle larger than normnal AOUT headers.