mktemp: add suffix handling

mktemp: add suffix handling

Now that mkstemps is supported, we might as well use it.

* src/mktemp.c (TMPDIR_OPTION): New enum value.
(longopts): Add new option.
(usage): Document it.
(count_trailing_X_s): Rename...
(count_consecutive_X_s): ...to this, and add parameter.
(mkstemp_len, mkdtemp_len): Add parameter.
(main): Implement new option.
(AUTHORS): Add myself.
* AUTHORS (mktemp): Likewise.
* tests/misc/mktemp: Test new option.
* doc/coreutils.texi (mktemp invocation): Document it.
* NEWS: Likewise.
Fixes http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=548316.