Visual C++ already declare the environ variable in the stdlib.h. So this redeclaratio...

Visual C++ already declare the environ variable in the stdlib.h. So this redeclaration cause a warning for this compiler. The declaration of this variable is now platform depend (WIN32 doesn't need this declaration). The pointer of the callback functions context default an context terminate are now exported in the Win32 dll.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@4841 48e7efb5-ca39-0410-a469-dd3cf9ba447f