Get the environment propagated to scons forked childs, and correct the dicom plugin about
a typedef of size_t that failed at least on x86_64-linux.

diff --git a/SConstruct b/SConstruct
index 16eccd9..603e931 100644
--- a/SConstruct
+++ b/SConstruct
@@ -7,8 +7,7 @@ else:
     cppflags = ['-O2']
     variant = 'Release'
 
-env = Environment(LIBPATH=[],
-                  CPPFLAGS = cppflags)
+env = Environment(ENV = os.environ)
 
 env['SBOX'] = False