* New feature <relevant> which is automatically deduced in most cases.
* Features which are not relevant do not affect target paths and
do not prevent merging of virtual targets.
* generators.jam: generator.run always returns usage-requirements
to allow usage-requirements in non-top-level generators. This
is necessary because we're using usage-requirements to track
relevance from flags.
* New rule toolset.uses-features to specify features that the rule
checks manually, instead of using toolset.flags. In the future,
we should consider restricting the properties actually passed,
to detect errors.
* Adjust tests to handle the new paths (verified by inspection).
* Add temporary option --ignore-relevance to consider all features relevant
to aid migration.
* New rule property.evaluate-conditional-relevance which helps tracking
relevance in <conditional>.
* Widely scattered changes to use the new interfaces.
* gcc.jam: Extend the 'toolset' feature with gcc here.
Use flags for linking too and eliminate 'link-options'
rule. Remove empty compile/archive/link/link-dll rules.
* toolset.jam (flags): Document somehow.
(set-target-variables): Call 'actualize' on values
of dependency features.
[SVN r16440]
* new/targets.jam (main-target.generate) Add extra path component to
virtual target which free properties are not equal to project's.
(basic-target.generate): Pass refined properties to 'construct'.
(virtual-target.extra-path): New rule.
(virtual-target.actualize): Make use of extra path.
* new/property.jam (take-free): New rule.
[SVN r14396]
* new/targets.jam (main-target.generate): Select the alternative
based on the list of non-free requirements.
* new/property.jam (remove-free): New rule, removes free property from
a property set.
[SVN r14391]
