* Rework the test case expansion.py to avoid interference from user-config.jam
and toolsets which previously masked this problem. Also add a test case
specifically for this issue.
* Remove the test case for BB60. I have no idea what BB60 is, but the test
case doesn't seem particularly important for the current implementation
given that project requirements are merged into the target requirements
long before conditionals are evaluated.
* feature.add-defaults: No longer accepts conditionals and returns
expanded properties. This matches the actual usage, and conditionals
never really worked right anyway.
* property.refine: Remove subfeatures of removed features.
* Moved property-set expansion and adding defaults into
targets.evaluate-requirements so that they correctly interact with
the target requirements.
* Expand subfeatures when matching target alternatives.
* Non-property-specific subfeatures like <cxxstd>11-iso are expanded correctly.
Various restructure of test framework handling of paths to avoid duplicate path editing which caused failed tests. Adjust many tests to deal with added subdirectories in build outputs now that toolset requirements are active.
