Add QgsDataProvider::invalidateConnections() and implement in Spatialite provider

This invalidates all cached connections to the given database name.
This will be used by the WFS provider to cleanup any cached connections before
removing its temporary Spatialite DB

(cherry-picked from 62bd406, necessary for offline plugin fix)

Author: rouault

python/core/qgsdataprovider.sip

@@ -218,6 +218,11 @@ class QgsDataProvider : QObject
      */
     virtual QgsError error() const;
 
+    /** Invalidate connections corresponding to specified name
+     * @note added in QGIS 2.16
+     */
+    virtual void invalidateConnections( const QString& connection );
+
   signals:
 
     /**

src/core/qgsdataprovider.h

@@ -306,6 +306,11 @@ class CORE_EXPORT QgsDataProvider : public QObject
      */
     virtual QgsError error() const { return mError; }
 
+    /** Invalidate connections corresponding to specified name
+     * @note added in QGIS 2.16
+     */
+    virtual void invalidateConnections( const QString& connection ) { Q_UNUSED( connection ); }
+
   signals:
 
     /**

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -5001,7 +5001,10 @@ const QgsField & QgsSpatiaLiteProvider::field( int index ) const
   return attributeFields[index];
 }
 
-
+void QgsSpatiaLiteProvider::invalidateConnections( const QString& connection )
+{
+  QgsSpatiaLiteConnPool::instance()->invalidateConnections( connection );
+}
 
 /**
  * Class factory to return a pointer to a newly created

src/providers/spatialite/qgsspatialiteprovider.h

@@ -233,6 +233,8 @@ class QgsSpatiaLiteProvider: public QgsVectorDataProvider
      */
     QgsAttributeList pkAttributeIndexes() override;
 
+    void invalidateConnections( const QString& connection ) override;
+
   signals:
     /**
      *   This is emitted whenever the worker thread has fully calculated the