Free SHM as soon as we dont need it anymore

If gammaray-client hangs (for whatever reason), it's parent process, the
launcher is still alive and doesn't release the SHM segment it owns. The
same happens when the launcher application crashes -- the SHM segment is
not released.

Each QSHM holds a QSystemSemaphore, and number of accessible semaphores
on a Unix system is very limited (128 is the upper limit).

If you've finally reached this limit, you can't create more SHM segments
and hence cannot start a GammaRay instance anymore.
You end up with this message:

void GammaRay::Launcher::sendProbeSettings() Failed to obtain shared
memory for probe settings: "QSharedMemoryPrivate::initKey: unable to set
key on lock" - error code (QSharedMemory::SharedMemoryError): 7

launcher/launcher.cpp

@@ -253,25 +253,28 @@ void Launcher::semaphoreReleased()
   m_safetyTimer.stop();
 
 #ifdef HAVE_SHM
-  SharedMemoryLocker locker(m_shm);
-  QByteArray ba = QByteArray::fromRawData(static_cast<const char*>(m_shm->data()), m_shm->size());
-  QBuffer buffer(&ba);
-  buffer.open(QIODevice::ReadOnly);
-
   quint16 port = 0;
-
-  while (Message::canReadMessage(&buffer)) {
-    const Message msg = Message::readMessage(&buffer);
-    switch (msg.type()) {
-      case Protocol::ServerPort:
-      {
-        msg.payload() >> port;
-        break;
+  {
+    SharedMemoryLocker locker(m_shm);
+    QByteArray ba = QByteArray::fromRawData(static_cast<const char*>(m_shm->data()), m_shm->size());
+    QBuffer buffer(&ba);
+    buffer.open(QIODevice::ReadOnly);
+
+    while (Message::canReadMessage(&buffer)) {
+      const Message msg = Message::readMessage(&buffer);
+      switch (msg.type()) {
+        case Protocol::ServerPort:
+        {
+          msg.payload() >> port;
+          break;
+        }
+        default:
+          continue;
       }
-      default:
-        continue;
     }
   }
+  delete m_shm;
+  m_shm = 0;
 
   if (port == 0) {
     qWarning() << "Unable to receive port number.";