Reverted specialization for trivial types

It caused too many problems. I left only specialiation for scalar types.
I will need to devise clever type traits for reconizing trivial types with working constructor.

test/Jamfile.v2

@@ -76,6 +76,5 @@ import testing ;
     [ run-fail optional_xconfig_NO_PROPER_CONVERT_FROM_CONST_INT_fail.cpp ]
     [ run optional_xconfig_NO_LEGAL_CONVERT_FROM_REF_pass.cpp ]
     [ compile-fail optional_xconfig_NO_LEGAL_CONVERT_FROM_REF_fail.cpp ]
-
   ;
 }