Bug 1062221 - Add a TypedList type and refactor mozbuild.util lists. r=gps
Bug 1062221 - Replace add_tier_dir with DIRS. r=gps
Bug 1062221 - Change how DIRS and TEST_DIRS are handled. r=gps

Up to now, DIRS and TEST_DIRS were dumb values. This change makes them
a list of ContextDerivedValues, and handles the fact that some types of
paths are relative to the current source directory and others to the
topsrcdir.

This also makes us one step closer to fixing bug 991983.
Bug 1063414 - Add infrastructure to follow what the current file being processed is in a Context. r=gps
Bug 1063414 - Move sandbox execution stack to context.Context. r=gps
Bug 1063414 - Make DIRS relative to the file they were added from. r=gps
Bug 1063432 - Do type coercion on sandbox function arguments. r=gps
Bug 1063437 - Use SourcePath smart type for sandbox includes. r=gps
Bug 1063437 - Remove MozbuildSandbox.normalize_path. r=gps