- Probable fix for #64.
  Introduce new option: LIBPE_OPT_OPEN_RW.
  This is used to decide which flags to pass to open(2) and mmap(2).
  For instance, we should only call open(2) with O_RDWR if we have
  permission to write the file we're analyzing. The same applies to
  mmap(2) with MAP_SHARED.
- Fix pe_err_e values. Duh!