Fix an issue with extremely large data identified by tjb900.

Due to the conversion from ssize_t to int we were losing bytes, and
ended up writing outside the receiver buffer. Similarly on the send,
due to the conversion to a lesser type, we could missinterpret the
end of the fragment.

opal/mca/btl/tcp/btl_tcp_frag.c

@@ -112,7 +112,7 @@ size_t mca_btl_tcp_frag_dump(mca_btl_tcp_frag_t* frag, char* msg, char* buf, siz
 
 bool mca_btl_tcp_frag_send(mca_btl_tcp_frag_t* frag, int sd)
 {
-    int cnt=-1;
+    ssize_t cnt = -1;
     size_t i, num_vecs;
 
     /* non-blocking write, but continue if interrupted */
@@ -145,7 +145,7 @@ bool mca_btl_tcp_frag_send(mca_btl_tcp_frag_t* frag, int sd)
     /* if the write didn't complete - update the iovec state */
     num_vecs = frag->iov_cnt;
     for(i=0; i<num_vecs; i++) {
-        if(cnt >= (int)frag->iov_ptr->iov_len) {
+        if(cnt >= (ssize_t)frag->iov_ptr->iov_len) {
             cnt -= frag->iov_ptr->iov_len;
             frag->iov_ptr++;
             frag->iov_idx++;
@@ -155,7 +155,7 @@ bool mca_btl_tcp_frag_send(mca_btl_tcp_frag_t* frag, int sd)
                 (((unsigned char*)frag->iov_ptr->iov_base) + cnt);
             frag->iov_ptr->iov_len -= cnt;
             OPAL_OUTPUT_VERBOSE((100, opal_btl_base_framework.framework_output,
-                                 "%s:%d write %d bytes on socket %d\n",
+                                 "%s:%d write %ld bytes on socket %d\n",
                                  __FILE__, __LINE__, cnt, sd));
             break;
         }
@@ -253,7 +253,7 @@ bool mca_btl_tcp_frag_recv(mca_btl_tcp_frag_t* frag, int sd)
     /* if the read didn't complete - update the iovec state */
     num_vecs = frag->iov_cnt;
     for( i = 0; i < num_vecs; i++ ) {
-        if( cnt < (int)frag->iov_ptr->iov_len ) {
+        if( cnt < (ssize_t)frag->iov_ptr->iov_len ) {
             frag->iov_ptr->iov_base = (opal_iov_base_ptr_t)
                 (((unsigned char*)frag->iov_ptr->iov_base) + cnt);
             frag->iov_ptr->iov_len -= cnt;