[C++-sig] Use alternative launcher for bpl-test rule

[John Reid]

Hi,

I'm having some problems asking boost.build to start the debugger or
valgrind when it runs some of my python extension bpl-test rules. I saw
in the boost.build code some comments that suggests it hijacks the
testing.launcher feature which I thought would be the way to do this.
Does anyone know if it is possible and what I should be doing?

Thanks,
John.