a68: make SET, CLEAR and TEST bits operators zero-based

a68: make SET, CLEAR and TEST bits operators zero-based

After some discussion at the working group we have decided that the
bits operators SET, CLEAR and TEST, which are a GNU extension, shall
get bit numbers which are zero-based rather than one-based.

Signed-off-by: Jose E. Marchesi <jemarch@gnu.org>
gcc/algol68/ChangeLog

	* a68-low-bits.cc (a68_bits_set): Make bit number zero-based rathe
	than one-based.
	(a68_bits_clear): Likewise.
	(a68_bits_test): Likewise.
	* ga68.texi (Extended bits operators): Adapt documentation
	accordingly.

gcc/testsuite/ChangeLog

	* algol68/execute/bits-clear-1.a68: Adapt test to new CLEAR
	semantics.
	* algol68/execute/bits-set-1.a68: Likewise for SET.
	* algol68/execute/bits-test-1.a68: Likewise for TEST.