+ add further log messages at startup for better troubleshooting, fix possible crash, fix typos

src/App/Application.cpp

@@ -922,7 +922,7 @@ void segmentation_fault_handler(int sig)
     switch (sig) {
         case SIGSEGV:
             std::cerr << "Illegal storage access..." << std::endl;
-            throw Base::Exception("Illegal storage access! Please save you work under a new file name and restart the application!");
+            throw Base::Exception("Illegal storage access! Please save your work under a new file name and restart the application!");
             break;
         case SIGABRT:
             std::cerr << "Abnormal program termination..." << std::endl;
@@ -945,7 +945,7 @@ void unexpection_error_handler()
 {
     std::cerr << "Unexpected error occurred..." << std::endl;
     // try to throw to give the user evantually a change to save 
-    throw Base::Exception("Unexpected error occurred! Please save you work under a new file name and restart the application!");
+    throw Base::Exception("Unexpected error occurred! Please save your work under a new file name and restart the application!");
 
     terminate();
 }
@@ -1207,6 +1207,7 @@ void Application::initApplication(void)
     UnitsApi::setSchema((UnitSystem)hGrp->GetInt("UserSchema",0));
 
     // starting the init script
+    Console().Log("Run App init script\n");
     Interpreter().runString(Base::ScriptFactory().ProduceScript("FreeCADInit"));
 }
 

src/Base/UnitsApi.cpp

@@ -80,16 +80,19 @@ UnitsApi::~UnitsApi()
 
 void UnitsApi::setSchema(UnitSystem s)
 {
-    if(UserPrefSystem){
+    if (UserPrefSystem) {
         UserPrefSystem->resetSchemaUnits(); // for schemas changed the Quantity constants
         delete UserPrefSystem;
+        UserPrefSystem = 0;
     }
     switch (s) {
         case SI1 : UserPrefSystem = new UnitsSchemaInternal(); break;
         case SI2 : UserPrefSystem = new UnitsSchemaMKS(); break;
         case Imperial1: UserPrefSystem = new UnitsSchemaImperial1(); break;
         case ImperialDecimal: UserPrefSystem = new UnitsSchemaImperialDecimal(); break;
+        default  : UserPrefSystem = new UnitsSchemaInternal(); s = SI1; break;
     }
+
     actSystem = s;
     UserPrefSystem->setSchemaUnits(); // if necesarry a unit schema can change the constants in Quantity (e.g. mi=1.8km rather then 1.6km).
 }

src/Gui/Application.cpp

@@ -1701,6 +1701,7 @@ void Application::runApplication(void)
 
     // running the GUI init script
     try {
+        Base::Console().Log("Run Gui init script\n");
         Base::Interpreter().runString(Base::ScriptFactory().ProduceScript("FreeCADGuiInit"));
     }
     catch (const Base::Exception& e) {

src/Main/FreeCADGuiPy.cpp

@@ -267,6 +267,7 @@ QWidget* setupMainWindow()
         static bool init = false;
         if (!init) {
             try {
+                Base::Console().Log("Run Gui init script\n");
                 Base::Interpreter().runString(Base::ScriptFactory().ProduceScript("FreeCADGuiInit"));
             }
             catch (const Base::Exception& e) {