Don't automatically commit all changes when editing a table column

Editing a table column in the Edit Table dialog accidentally committed
all prior changes to the database, effectively clicking the 'Write
Changes' button while working on the table. This is no problem if your
working on a clean database, but is a problem if you have made other
changes before. In the latter case you lose the ability to roll them
back and you can't use the Cancel button in the Edit Table dialog
anymore.

See issue #1116.

src/sqlitedb.cpp

@@ -1414,7 +1414,13 @@ bool DBBrowserDB::setPragma(const QString& pragma, const QString& value)
     // Set the pragma value
     QString sql = QString("PRAGMA %1 = \"%2\";").arg(pragma).arg(value);
 
-    releaseSavepoint();
+    // In general, we want to commit changes before running pragmas because most of them can't be rolled back and some of them
+    // even fail when run in a transaction. However, the defer_foreign_keys pragma has neither problem and we need it to be settable
+    // inside transactions (see the renameColumn() function where it is set and reset at some point and where we don't want the changes
+    // to be committed just because of this pragma).
+    if(pragma != "defer_foreign_keys")
+        releaseSavepoint();
+
     bool res = executeSQL(sql, false, true); // PRAGMA statements are usually not transaction bound, so we can't revert
     if( !res )
         qWarning() << tr("Error setting pragma %1 to %2: %3").arg(pragma).arg(value).arg(lastErrorMessage);