Add new 'z' format for print command.

  http://sourceware.org/ml/gdb-patches/2013-07/msg00235.html

gdb/ChangeLog

        * NEWS: Mention new 'z' formatter.
        * printcmd.c (print_scalar_formatted): Add new 'z' formatter.
        (_initialize_printcmd): Mention 'z' formatter in help text of the
        'x' command.

gdb/doc/ChangeLog

        * gdb.texinfo (Output Formats): Mention the new 'z' formatter.

gdb/testsuite/ChangeLog

        * gdb.base/printcmds.exp (test_print_int_arrays): Add tests for x,
        z, o, and t output formats.
        * gdb.base/display.exp: Use 'k' as an undefined format now that
        'z' is defined.
Resue 'z' formatter from mi register display code.

  http://sourceware.org/ml/gdb-patches/2013-07/msg00236.html

gdb/ChangeLog

        * mi/mi-main.c (output_register): Make MI 'r' format use standard
        'z' format code.  Remove error for optimized out values, standard
        code will handle these fine.

gdb/testsuite/ChangeLog

        * gdb.mi/mi-reg-undefined.exp: New file.
        * gdb.mi/mi-reg-undefined.c: Likewise.
        * gdb.mi/mi-reg-undefined.S: Likewise.