Unsigned comparison to 0 warning avoidance (#869)

* Added int variable for comparison with H5_VERS_RELEASE in H5.c to avoid
warning that unsigned comparison < 0 is always false, which is known,
        but for later versions the comparison can possibly be true.

* Better solution for avoiding warning that unsigned comparison < 0.

src/H5.c

@@ -824,7 +824,11 @@ H5check_version(unsigned majnum, unsigned minnum, unsigned relnum)
             disable_version_check = (unsigned int)HDstrtol(s, NULL, 0);
     }
 
-    if (H5_VERS_MAJOR != majnum || H5_VERS_MINOR != minnum || H5_VERS_RELEASE != relnum) {
+    /* H5_VERS_MAJOR and H5_VERS_MINOR must match */
+    /* Cast relnum to int to avoid warning for unsigned < 0 comparison
+     * in first release versions */
+    if (H5_VERS_MAJOR != majnum || H5_VERS_MINOR != minnum || H5_VERS_RELEASE > (int)relnum) {
+
         switch (disable_version_check) {
             case 0:
                 HDfprintf(stderr, "%s%s", version_mismatch_warning,