Remove compiler warnings on Solaris 8.
Can go into 2.2.x, but not necessary.
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
index 3232e57..3153693 100644
--- a/Modules/pyexpat.c
+++ b/Modules/pyexpat.c
@@ -1366,7 +1366,7 @@
     char *rev = rcsid;
     int i = 0;
 
-    while (!isdigit(*rev))
+    while (!isdigit((int)*rev))
         ++rev;
     while (rev[i] != ' ' && rev[i] != '\0')
         ++i;