win32: embedding of the compiler, use boost 1_54

- MinGW is now part of the vle binaries (Closes #132)
- MinGW is set into the path before launching cmake. It is now
useless to set VLE into the path during installation (Closes #89).
- boost 1_54 is used (instead of boost 1_53)
win32: embedding cmake

- on win32 cmake is embedded into the VLE install
- add cmake.exe into the path before launchin any process on win32
- provides the function findProgram into the Path class; for cmake on
  win32, computes the absolute path (should fix #92, Closes#92)
utils: add Package configure option WITH_WARNINGS

a warning option (defaut to OFF for win32, ON otherwise) is added in vle.conf.
Iff OFF all warnings are disabled.