Allow walking/caching more than main::

[rocky]

Here is a scenario of from B::CodeLines. I want to give a file or Perl Module and get a list of the traceable line numbers. For a main problem this works pretty well. But what if I start with a Perl module?

B::Utils seems to be geared for main programs: walksymtable() inside _init_sub_cache() passes main:: unconditionally. I think a number of times one also wants to do the same kind of thing for a module. For example, supposed there is an Enbugger->stop, inside a module. Because of B::Utils main package orientation, I don't think you will pick up the line numbers of methods inside that package.