Ensure referent data doesn't go out of scope for StringRef/Twine

- Fixes #7

Author: virtuald

wpiutil/src/type_casters/wpi_stringref_type_caster.h

@@ -32,6 +32,9 @@ struct type_caster<wpi::StringRef>
 
         // this assumes that the stringref won't be retained after the function call
         value = wpi::StringRef(data, size);
+
+        // src must be valid as long as this loader is valid
+        loader_life_support::add_patient(src);
         return true;
     }
 

wpiutil/src/type_casters/wpi_twine_type_caster.h

@@ -39,6 +39,9 @@ struct type_caster<wpi::Twine>
 
         // this assumes that the stringref won't be retained after the function call
         ref = wpi::StringRef(data, size);
+
+        // src must be valid as long as this loader is valid
+        loader_life_support::add_patient(src);
         return true;
     }