Apply feature defaults when building.
* new/build-request.jam (expand-with-defaults): New rule
* new/build-system.jam, new/targets.jam: Use 'expand-with-defaults' instead
of 'expand'.
* new/builtin.jam: Define new feature 'threading'.
* test/project_test3.py: Test that feature defaults are applied.
[SVN r14307]
Vladimir Prus