This fixes the second problem identified by Mantis bug #548.
compiler/ml_tag_switch.m:
Detect the circumstances in which this problem would arise.
In such cases, simply fail, and let ml_switch_gen.m fall back
to implementing the switch as an if-then-else chain.
compiler/ml_switch_gen.m:
Implement that fallback.
compiler/switch_util.m:
The new code in ml_tag_switch.m needs to thread a fourth piece of state
through the predicate it passes to group_cases_by_ptag, so change
its argument list to accommodate such predicates. And since some other
modules pass the same predicates to group_cases_by_ptag and
string_binary_cases, make the same change in the argument list
of that predicate as well.
Delete one stray comment, and note that another comment seems misplaced.
compiler/ml_string_switch.m:
compiler/string_switch.m:
compiler/switch_case.m:
compiler/tag_switch.m:
Conform to the changes in switch_util.m.
tests/hard_coded/bug548.exp:
tests/hard_coded/Mmakefile:
Enable the previously-added test case for Mantis #548, after
add an .exp file for it.
