Initial, partial, try at common build for distribution targets.

svn path=/branches/build_for_distribution/boost/tools/build/; revision=19170
More on build_for_distribution staging...
- Jamfile; added stage for header files tree.
- Jamfile; commented out some targets that fail to build.
- tools/build/boost-base.jam; fixed file-close duplication.
- tools/build/boost-base.jam; added <tree-subdirs> to stage rule to preserve tree structure of a tree of files (like headers).

svn path=/branches/build_for_distribution/boost/tools/build/; revision=19182
All parts of the build-for-distribution build functionality implemented.
- Moved the common functionality to boost-base.jam
- Handle some common options for controlling install location.
- Add <locate> to stage so that the stage can be relocated anywhere in the FS.
- Added documentation for common-stage-tag.

svn path=/branches/build_for_distribution/boost/tools/build/; revision=19232
Minor fixes after testing in Linux of build_for_distribution build code.
- Jamfile; added check for python configuration.
- tools/build/boost-base.jam; Fixed toolset version number duplication.
- tools/build/boost-base.jam; Fixed unless/cond argument signatures.
- tools/build/boost-base.jam; Fixed calculation of architecture subdir in stage when the default is "default".

svn path=/branches/build_for_distribution/boost/tools/build/; revision=19233