message: Add GetText()/SetText() methods to more CMessage types.
  They are aliases for existing methods, to simplify code reuse.
diff: @@ -275,6 +275,8 @@ class CKickMessage : public CTargetMessage {
  void SetKickedNick(const CString& sNick) { SetParam(1, sNick); }
  CString GetReason() const { return GetParam(2); }
  void SetReason(const CString& sReason) { SetParam(2, sReason); }
  + CString GetText() const { return GetReason(); }
  + void SetText(const CString& sText) { SetReason(sText); }
  };
  REGISTER_ZNC_MESSAGE(CKickMessage);
  @@ -282,6 +284,8 @@ class CPartMessage : public CTargetMessage {
  public:
  CString GetReason() const { return GetParam(1); }
  void SetReason(const CString& sReason) { SetParam(1, sReason); }
  + CString GetText() const { return GetReason(); }
  + void SetText(const CString& sText) { SetReason(sText); }
  };
  REGISTER_ZNC_MESSAGE(CPartMessage);
  @@ -289,6 +293,8 @@ class CQuitMessage : public CMessage {
  public:
  CString GetReason() const { return GetParam(0); }
  void SetReason(const CString& sReason) { SetParam(0, sReason); }
  + CString GetText() const { return GetReason(); }
  + void SetText(const CString& sText) { SetReason(sText); }
  };
  REGISTER_ZNC_MESSAGE(CQuitMessage);
  @@ -303,6 +309,8 @@ class CTopicMessage : public CTargetMessage {
  public:
  CString GetTopic() const { return GetParam(1); }
  void SetTopic(const CString& sTopic) { SetParam(1, sTopic); }
  + CString GetText() const { return GetTopic(); }
  + void SetText(const CString& sText) { SetTopic(sText); }
  };
  REGISTER_ZNC_MESSAGE(CTopicMessage);
  