Log Message:
RELEASE 2.5.0 - Mon, 09 Apr 2016 11:27:42 -0700
- Removed a lot of compatibility methods and workarounds
  for Python versions < 2.7, in order to prepare the work
  towards a combined 2.7/3.x version.
  Also fixed the default arguments for the print_tree and
  render_tree methods.
- Added support for cross-language dependency scanning;
  SCons now respects scanner keys for implicit dependencies.
  - Notes for SCons users with heterogeneous systems.
    - May find new (previously missed) dependencies.
    - May cause rebuild after upgrade due to dependency changes.
    - May find new dependency errors (EG. cycles).
      - Discovered in some of the SCons QT tests.
- Resolved missing cross-language dependencies for
  SWIG bindings
- Corrected typo in User Guide for Scanner keyword.
- Install builder interacts with scanner found in SCANNERS differently.
  - Previous: Install builder recursively scanned implicit dependencies
    for scanners from SCANNER, but not for built-in (default) scanners.
  - Current: Install builder will not scan for implicit dependencies via
    either scanner source. This optimizes some Install builder behavior
    and brings orthogonality to Install builder scanning behavior.
- Add better messaging when two environments have
  different actions for the same target
- Fix issue only with MSVC and Always build where targets
  marked AlwaysBuild wouldn't make it into CHANGED_SOURCES
  and thus yield an empty compile command line.
- Fix posix platform escaping logic to properly handle paths
  with parens in them "()".
- Intel Compiler 2016 (Linux/Mac) update for tool directories.
- Fix for issue 2494: Added string support for Chmod function.
- change cache to use 2 character subdirectories, rather than one character,
  so as not to give huge directories for large caches, a situation which
  causes issues for NFS.
  For existing caches, you will need to run the scons-configure-cache.py
  script to update them to the new format. You will get a warning every time
  you build until you co this.
- Fix a bunch of unit tests on windows