tests/valid_make_int/bug506.m:
tests/valid_make_int/bug506_sub.m:
The test case. bug506_sub.m defines a type whose name is a Mercury
operator; we test whether the compiler can read its .int3 file
when generating the .int file of bug506.m.
tests/valid_make_int/Mmakefile:
Enable the new case, after adding infrastructure for handling
multi-module programs.
