Fix location of bootstrap log on Windows.

Thanks to Chris Nogradi for the report.
Make installation of Boost.Build work again.

It needs further work, to avoid $prefix/share/boost-build/src
and put everything directly under $prefix/share/boost-build
and to put examples under $prefix/share/doc/boost-build or
similar.
Minor changes in feature.py.
Prevent hard error when creating a property from string, in case string references an unknown feature.
Removed unused var.
Add support for --hash.
Removed porting error which flattens property set into strings.
Fix tag rule for searched libs.
Resurrect c++-template-depth feature.
Fix some porting errors in msvc.py. Created a new action which allows us to change sources for target as well as decide on the actions name at the last moment. This is needed by MSVC PCH targets.
Fix some porting errors in common.py.
Ported boost.jam module.
Fix syntax errors in rc.py and midl.py.
Fix a bug causing invalid composite features due to a missing expand call.
Fix mixed slash/backslash in actions.
Fix some trivial syntax/runtime errors in stage.py.
Fix increasing indent when running --debug-generators.
Fix typo in comment.
Add Python port test results.

Storing those in git is not perfect, but we need to have
baseline results known, and it's the easiest approach.
Merge improvements from Juraj, as follows:

      Minor changes in feature.py.
      Prevent hard error when creating a property from string,
         in case string references an unknown feature.
      Removed unused var.
      Add support for --hash.
      Removed porting error which flattens property set into strings.
      Fix tag rule for searched libs.
      Resurrect c++-template-depth feature.
      Fix some porting errors in msvc.py. Created a new action which
         allows us to change sources for target as well as decide on
         the actions name at the last moment. This is nee
      Fix some porting errors in common.py.
      Ported boost.jam module.
      Fix syntax errors in rc.py and midl.py.
      Fix a bug causing invalid composite features due to a missing
         expand call.
      Fix mixed slash/backslash in actions.
      Fix some trivial syntax/runtime errors in stage.py.
      Fix increasing indent when running --debug-generators.