a68: add TEST operator for bits to expanded prelude

a68: add TEST operator for bits to expanded prelude

This patch adds support for a TEST operator for L bits.  Documentation
and tests are included.

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

	* a68.h: Prototypes for a68_bits_test and a68_lower_test3.
	* a68-low-bits.cc (a68_bits_test): New function.
	* a68-low-prelude.cc (a68_lower_test3): Likewise.
	* a68-parser-prelude.cc (gnu_prelude): Declare TEST operators and
	their priority.
	* ga68.texi (Extended bits operators): New section.

gcc/testsuite/ChangeLog

	* algol68/execute/bits-test-1.a68: New test.