Presumed correct compiler pass for future statements

XXX still need to integrate into symtable API

compile.h: Remove ff_n_simple_stmt; obsolete.

           Add ff_found_docstring used internally to skip one and only
           one string at the beginning of a module.

compile.c: Add check for from __future__ imports to far into the file.

 	   In symtable_global() check for -1 returned from
	   symtable_lookup(), which signifies name not defined.

	   Add missing DECERF in symtable_add_def.

           Free c->c_future.

future.c:  Add special handling for multiple statements joined on a
	   single line using one or more semicolons; this form can
           include an illegal future statement that would otherwise be
           hard to detect.

	   Add support for detecting and skipping doc strings.

Include/compile.h

@@ -51,8 +51,8 @@ DL_IMPORT(int) PyCode_Addr2Line(PyCodeObject *, int);
 /* Future feature support */
 
 typedef struct {
+    int ff_found_docstring;
     int ff_last_lineno;
-    int ff_n_simple_stmt;
     int ff_nested_scopes;
 } PyFutureFeatures;