Reinstate PUSHS clearing the SECTION scope (#870)

* Reinstate PUSHS clearing the SECTION scope

Otherwise you can use `PUSHS` to simulate the old `ds -21`, and possibly cause bugs

* Have PUSHS push LOAD block state as well

It does not make sense not to, and coud cause bugs.

src/asm/output.c

@@ -53,8 +53,7 @@ struct Assertion {
 
 char *objectName;
 
-/* TODO: shouldn't `currentSection` be somewhere else? */
-struct Section *sectionList, *currentSection;
+struct Section *sectionList;
 
 /* Linked list of symbols to put in the object file */
 static struct Symbol *objectSymbols = NULL;