run-tests: fix get port to try differing ports

The code was moving its offset each time through the loop,
but because it failed to update port, the port was not
going to be available...

tests/run-tests.py

@@ -2015,11 +2015,11 b' class TestRunner(object):'
     def _getport(self, count):
         port = self._ports.get(count) # do we have a cached entry?
         if port is None:
-            port = self.options.port + self._portoffset
             portneeded = 3
             # above 100 tries we just give up and let test reports failure
             for tries in xrange(100):
                 allfree = True
+                port = self.options.port + self._portoffset
                 for idx in xrange(portneeded):
                     if not checkportisavailable(port + idx):
                         allfree = False

tests/test-run-tests.t

@@ -223,6 +223,20 b' Verify that when a process fails to star'
   [1]
   $ rm test-serve-fail.t
 
+Verify that we can try other ports
+===================================
+  $ hg init inuse
+  $ hg serve -R inuse -p $HGPORT -d --pid-file=blocks.pid
+  $ cat blocks.pid >> $DAEMON_PIDS
+  $ cat > test-serve-inuse.t <<EOF
+  >   $ hg serve -R `pwd`/inuse -p \$HGPORT -d --pid-file=hg.pid
+  >   $ cat hg.pid >> \$DAEMON_PIDS
+  > EOF
+  $ rt test-serve-inuse.t
+  .
+  # Ran 1 tests, 0 skipped, 0 warned, 0 failed.
+  $ rm test-serve-inuse.t
+
 Running In Debug Mode
 ======================