Scons tool: add windows7 scons example
SConscript: fix script if config has section 'COMMON'
SConstruct: add common paths to env
SConstruct: manage C++ environment for win
Sconscript: base envJava and envPy on C++ environment

Create java and python environments is simplier.
SConstruct: fix win build by adding python to LIBPATH
SConscript: clean

Remove duplicate variable on C++ environment.
SConscript: clean how to check libav when unix
Merge pull request #67 from cchampet/build_windows

Build windows