Fix grabbing of BOOST_BUILD_PATH from environment

svn path=/trunk/tools/build/v2/; revision=64354
Fix project loading.

- If we have Jamroot and Jamfile, load both
- Actually inherit build-dir from parent.

svn path=/trunk/tools/build/v2/; revision=64355
Make build-dir project attribute and command-line option work.

svn path=/trunk/tools/build/v2/; revision=64357
Respect '<build>no'.

svn path=/trunk/tools/build/v2/; revision=64358
When refining properties, actually remove properties that are overridden.

svn path=/trunk/tools/build/v2/; revision=64359
Respect --debug-building.

svn path=/trunk/tools/build/v2/; revision=64360
Add bjam_signature for feature.compose and feature.subfeature.

svn path=/trunk/tools/build/v2/; revision=64361
Robustify feature.is_implicit_value.

svn path=/trunk/tools/build/v2/; revision=64362
Export the 'variant' rule to Jamfiles

svn path=/trunk/tools/build/v2/; revision=64363
Fix removing of parent project requirements

svn path=/trunk/tools/build/v2/; revision=64364
Use Property, not string, in more places

svn path=/trunk/tools/build/v2/; revision=64382
Make default build work.

Also, return non-zero status if there were errors.

svn path=/trunk/tools/build/v2/; revision=64384
More changes

svn path=/trunk/tools/build/v2/; revision=64406
Fix header dependencies processing.

svn path=/trunk/tools/build/v2/; revision=64407
More header dependencies fixes

svn path=/trunk/tools/build/v2/; revision=64408
Various fixes

svn path=/trunk/tools/build/v2/; revision=64426
Fix requesting specific files on the command line

svn path=/trunk/tools/build/v2/; revision=64427
Update virtual_target.py

svn path=/trunk/tools/build/v2/; revision=64428
Don't pass None for property set

svn path=/trunk/tools/build/v2/; revision=64429
Port notfile.py. Attempt to clean the mess with decorating action names.

svn path=/trunk/tools/build/v2/; revision=64431