SI-6888 Loosen criteria for $outer search.

In order to cater for nested classes with names that end
with '$', which lead to ambiguity when unmangling expanded
names.

In:

    class X { object $ }

We end up with:

    orginalName(X$$$$$outer) = $$$outer

This change modifies `outerSource` to consider that to be
and outer accessor name. It is a piecemeal fix, and no doubt
there are other nasty surprises in store for those inclined to
flash their $$$ in identifier names, but the method changed is
not used widely and this solves the reported problem.

SI-2806 remains open to address the deeper problem.