1. 'componentsConfigs' no longer is a graph identified by
    ComponentNames, but by ComponentIds (this is because, eventually,
    they'll be identified uniquely by a UnitId, but NOT by a
    ComponentName.) This caused some modest use-site changes but nothing
    major.

2. To make it easier to get the Component given a ComponentLocalBuildInfo,
   I added a new field 'componentLocalName' which records the original
   source-level name of the 'ComponentLocalBuildInfo'.

3. Rewrote the test in 'depLibraryPaths' which checks if a component
   is "internal" or not (arguably this should be factored into a common
   function, but at the moment it only occurs in one place.)

4. Finally, 'depLibraryPaths' correctly takes the transitive closure
   of internal dependencies (rather than assuming that an internal
   dependency must be on the public library).

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>