Fix memory leak with custom importer not being freed

Author: mgreter

sass_context.cpp

@@ -549,9 +549,12 @@ extern "C" {
         cur = next;
       }
     }
+    // Free custom importer
+    free(options->importer);
     // Free the list container
     free(options->c_functions);
     // Make it null terminated
+    options->importer = 0;
     options->c_functions = 0;
     options->include_paths = 0;
   }

sass_functions.cpp

@@ -66,6 +66,12 @@ extern "C" {
   Sass_C_Import_Fn sass_import_get_function(Sass_C_Import_Callback fn) { return fn->function; }
   void* sass_import_get_cookie(Sass_C_Import_Callback fn) { return fn->cookie; }
 
+  // Just in case we have some stray import structs
+  void sass_delete_importer (Sass_C_Import_Callback fn)
+  {
+    free(fn);
+  }
+
   // Creator for sass custom importer return argument list
   struct Sass_Import** sass_make_import_list(size_t length)
   {

sass_functions.h

@@ -28,6 +28,8 @@ Sass_C_Import_Callback sass_make_importer (Sass_C_Import_Fn, void* cookie);
 Sass_C_Import_Fn sass_import_get_function (Sass_C_Import_Callback fn);
 void* sass_import_get_cookie (Sass_C_Import_Callback fn);
 
+// Deallocator for associated memory
+void sass_delete_importer (Sass_C_Import_Callback fn);
 
 // Creator for sass custom importer return argument list
 struct Sass_Import** sass_make_import_list (size_t length);