PR 2257

PR 2257
* elfcode.h (elf_object_p): Allow files with corrupt e_shstrndx fields to
  still be handled as ELF files.
* readelf.c (SECTION_NAME): Cope with a missing string table.
  (process_file_header): Cope with a corrupt e_shstrndx field.
  (process_section_headers): Correctly handle an e_shstrndx value of SHF_UNDEF.