Misc. typos

src/App/Application.cpp

@@ -1015,7 +1015,7 @@ void Application::destruct(void)
     _pcSysParamMngr = 0;
     _pcUserParamMngr = 0;
 
-    // not initialized or doubel destruct!
+    // not initialized or double destruct!
     assert(_pcSingleton);
     delete _pcSingleton;
 

src/App/Expression.cpp

@@ -1876,7 +1876,7 @@ std::vector<boost::tuple<int, int, std::string> > tokenize(const std::string &st
   * returned expression. If the parser fails for some reason, and exception is thrown.
   *
   * @param owner  The DocumentObject that will own the expression.
-  * @param buffer The sting buffer to parse.
+  * @param buffer The string buffer to parse.
   *
   * @returns A pointer to an expression.
   *

src/App/ExtensionContainer.cpp

@@ -288,7 +288,7 @@ void ExtensionContainer::onChanged(const Property* prop) {
 void ExtensionContainer::Save(Base::Writer& writer) const {
 
     //Note: save extensions must be called first to ensure that the extension element is always the 
-    //      very first inside the object element. That is needed as extension eleent works together with 
+    //      very first inside the object element. This is needed since extension element works together with 
     //      an object attribute, and if another element would be read first the object attributes would be
     //      cleared.
     saveExtensions(writer);