Test: fixed osx "leaks" support in test.

Due to changes in recent releases of osx leaks utility, the osx leak
detection no longer worked. Now it is fixed in a way that should be
backward compatible.

tests/support/server.tcl

@@ -38,7 +38,9 @@ proc kill_server config {
             if {[string match {*Darwin*} [exec uname -a]]} {
                 tags {"leaks"} {
                     test "Check for memory leaks (pid $pid)" {
-                        exec leaks $pid
+                        set output {0 leaks}
+                        catch {exec leaks $pid} output
+                        set output
                     } {*0 leaks*}
                 }
             }