[Backport] Provide missing implementation of PythonQtSlotInfo::getGlobalShouldAllowThreads() (#65)

(cherry picked from commit MeVisLab/pythonqt@b7c1512)

Author: githubuser0xFFFF

src/PythonQtMethodInfo.cpp

@@ -654,3 +654,8 @@ void PythonQtSlotInfo::setGlobalShouldAllowThreads(bool flag)
 {
   _globalShouldAllowThreads = flag;
 }
+
+bool PythonQtSlotInfo::getGlobalShouldAllowThreads()
+{
+  return _globalShouldAllowThreads;
+}