* new/targets.jam
(main-target.select-alternative): Rewrite.
(main-target.generate-really): Issue error in all cases where best
alternative could not be found.
(basic-target.match): Renamed from 'match-rank' and changed.
* boost_build_v2.html: Document new algorithm.
* test/alternatives.py: More tests.
[SVN r20331]
* new/targets.jam
(generate): Use a special string to report failure, not just return
of empty list.
(basic-target.generate-sources): Accomodate the above change.
(basic-target.check-for-unused-sources): Allow empty list of targets.
* test/alternatives.py: New test.
[SVN r17906]
* new/targets.jam
(main-target.default-build): New field.
(main-target.add-alternative): Don't allow default-build for
second and subsequence alternatives. Record default build
from the first one.
(main-target.generate): Expand build request.
(main-target.generate-really): New rule, extracted from 'generate'.
(basic-target.default-build): New rule.
(basic-target.generate): Don't expand default build.
* test/BoostBuild.py
Allow to suppress passing toolset when calling run_build_system.
Some Python 2.1 compatibility fixes.
* test/alternatives.py
More tests.
* test/default_build.py
More tests.
[SVN r17683]
* new/targets.jam
(main-target.select-alternatives): New rule.
(main-target.generate): Simplify, using the above.
* new/errors.jam
(error): Do EXIT if --no-error-backtrace is given.
* tests/alternatives.py: New test.
[SVN r17673]
