Fix signedness of various char variables to stop causing a warning under gcc 4.
diff --git a/Python/compile.c b/Python/compile.c
index 5781b21..476dbe6 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -662,7 +662,7 @@
 
 	/* Bypass optimization when the lineno table is too complex */
 	assert(PyString_Check(lineno_obj));
-	lineno = PyString_AS_STRING(lineno_obj);
+	lineno = (unsigned char*)PyString_AS_STRING(lineno_obj);
 	tabsiz = PyString_GET_SIZE(lineno_obj);
 	if (memchr(lineno, 255, tabsiz) != NULL)
 		goto exitUnchanged;