Applied patch [ 651287 ] adds missing wxTreeCtrl::GetEditControl

Applied patch [ 651287 ] adds missing wxTreeCtrl::GetEditControl

This patch implements a missing member in the generic
version of the wxTreeCtrl. The GetEditControl member is
currently not implemented in the generic tree control
used by wxGTK. This patch implements the feature by

1. adding a pointer to the wxTextTreeControl as a
member (m_textCtrl) of the wxGenericTreeCtrl class
2. making sure pointer was initialized to 0
3. using the member variable instead of the stack
variable in the wxGenericTreeCtrl::Edit member
4. making sure the new wxGenericTreeCtrl class
member is set to 0 when the control is set up for
deletion in Finish by calling a new protected member
(ResetTextControl) of the wxGenericTreeCtrl class.

These modification were discussed on the wx-dev list
under the "wxGTK - wxTreeCtrl::GetEditControl status?"
subject.

I have tested, but I certainly welcome comments and
further testing.

Pete Stieber

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18192 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775