Add new program: truncate

Add new program: truncate

* AUTHORS: Register as the author
* NEWS: Mention this change
* README: Add truncate command to list
* src/truncate.c: New command
* src/Makefile.am: Add truncate command to list to build
* src/.gitignore: Add truncate binary to list to ignore
* doc/coreutils.texi (truncate invocation): Add truncate info
* man/Makefile.am: Add truncate man page to list to build
* man/truncate.x: Add truncate man page template
* po/POTFILES.in: Add truncate to list to translate
* tests/Makefile.am: Add truncate tests
* tests/misc/help-version: Add support for new truncate command
* tests/misc/truncate-dangling-symlink: check dangling link ok
* tests/misc/truncate-dir-fail: ensure dirs fail
* tests/misc/truncate-fail-diag: validate messages for missing paths
* tests/misc/truncate-fifo: ensure fifos ignored
* tests/misc/truncate-no-create-missing: ensure -c option honoured
* tests/misc/truncate-overflow: check signed integer overflows
* tests/misc/truncate-owned-by-other: root permissions check
* tests/misc/truncate-parameters: check invalid parameter combinations
* tests/misc/truncate-relative: check invalid relative sizes