Merge branch 'develop'

* develop:
  Fix location of bootstrap log on Windows.
  Ignore build directories
  Fix mdash->emdash typo that broke documentation build.
Merge branch 'develop'

* develop:
  Make installation of Boost.Build work again.
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Python Port: Make importing a little more robust.

- create a b2.<whatever> index for O(1) package/module searching.
- make the .pyc's sit next to their respective files; preventing
  pollution of workspace
- restore the __file__ variable for imported files
- prevent importing the same module twice under two separate names;
  also preventing running initialization code twice (registering types
  and features)
- create an __init__.py for the contrib directory
- requires Python 2.3 or newer for pkgutil
Add get_target_variable to engine interface.
Make sure all of BOOST_BUILD_PATH is checked for module importing.
Merge pull request #32 from frenchtoast747/features/python-module-import

Python Port: Make importing more robust.
Merge branch 'master' of https://github.com/boostorg/build into develop