fix wxTextCtrl::Replace() under wxGTK; added unit test for it and describe its effect on the insertion point

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57253 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/textctrl.h

@@ -1476,6 +1476,9 @@ public:
         Removes the text starting at the first given position up to
         (but not including) the character at the last position.
 
+        This function puts the current insertion point position at @a to as a
+        side effect.
+
         @param from
             The first position.
         @param to
@@ -1487,6 +1490,9 @@ public:
         Replaces the text starting at the first position up to
         (but not including) the character at the last position with the given text.
 
+        This function puts the current insertion point position at @a to as a
+        side effect.
+
         @param from
             The first position.
         @param to