Fix %zd string formatting on Mac OS X so it prints negative numbers.

In addition to testing positive numbers, verify negative numbers work in configure.
In order to avoid compiler warnings on OS X 10.4, also change the order of the check
for the format character to use (PY_FORMAT_SIZE_T) in the sprintf format
for Py_ssize_t.  This patch changes PY_FORMAT_SIZE_T from "" to "l" if it wasn't
defined at configure time.  Need to verify the buildbot results.

Backport candidate (if everyone thinks this patch can't be improved).
diff --git a/configure b/configure
index b96349a..ecbdf26 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 51173 .
+# From configure.in Revision: 51727 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.59 for python 2.6.
 #
@@ -22110,12 +22110,26 @@
 
 int main()
 {
-    char buffer[4];
+    char buffer[256];
+
+#ifdef HAVE_SSIZE_T
+typedef ssize_t Py_ssize_t;
+#elif SIZEOF_VOID_P == SIZEOF_LONG
+typedef long Py_ssize_t;
+#else
+typedef int Py_ssize_t;
+#endif
 
     if(sprintf(buffer, "%zd", (size_t)123) < 0)
        	return 1;
 
-    if (strncmp(buffer, "123", 3))
+    if (strcmp(buffer, "123"))
+	return 1;
+
+    if (sprintf(buffer, "%zd", (Py_ssize_t)-123) < 0)
+       	return 1;
+
+    if (strcmp(buffer, "-123"))
 	return 1;
 
     return 0;