CmdModify: Reorganize code for reuse

- Get "modify" checks ready for reuse by CmdImport's newly added update
  support.
- No changes in functionality, code reorganization only.

src/commands/CmdModify.h

@@ -35,6 +35,13 @@ class CmdModify : public Command
 public:
   CmdModify ();
   int execute (std::string&);
+  void checkConsistency (Task &before, Task &after);
+  int modifyAndUpdate (Task &before, Task &after,
+    std::map <std::string, std::string> *projectChanges = NULL);
+  int modifyRecurrenceSiblings (Task &task,
+    std::map <std::string, std::string> *projectChanges = NULL);
+  int modifyRecurrenceParent (Task &task,
+    std::map <std::string, std::string> *projectChanges = NULL);
 };
 
 #endif