Module Resolver roots

[Jonathan Gibbons]

Mark,

The current module Resolver only takes a single root at a time.  Unless 
I'm missing
something, this makes it hard to resolve a group of mutually dependent 
modules.
While the runtime may be able to have a limited view of a root (i.e. the 
module
containing the main class), javac needs a somewhat more liberal view.  javac
currently determines the set of roots to be those module-info files 
given on the
command line, together with the module-info files from the source path 
that are
required by the other compilation units on the command line.

It would help if the next round of Resolver API could take a set of 
roots, instead of just
one.

-- Jon