64 bit PPC bug fix. So small, yet wrecks such havoc.

This commit was SVN r6204.

src/mca/ptl/base/ptl_base_sendreq.h

@@ -58,7 +58,7 @@ static inline void mca_ptl_base_send_request_offset(
     mca_ptl_base_send_request_t* request,
     size_t offset)
 {
-    OMPI_THREAD_ADD32((int32_t*)(&request->req_offset), offset);
+    OMPI_THREAD_ADD32((size_t*)(&request->req_offset), offset);
 }