Don't use text control foreground colour for generic wxSearchCtrl itself.

Don't use text control foreground colour for generic wxSearchCtrl itself.

Logically, it should be done in the other direction and also doing it like
this means that the search and cancel icons, rendered using the current
foreground colour, are barely visible when using generic wxTextCtrl::SetHint()
implementation, as in wxGTK, because the text control foreground is set to
light grey in this case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72580 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775