Applied patch [ 621451 ] Fixed version of wxSlider class

Applied patch [ 621451 ] Fixed version of wxSlider class
Otto Wyss

This patch corrects several bugs in the wxSlider class
for the wxUniversal/MSW port. It affects the files
"slider.h", "slider.cpp", "win32.cpp" and "gtk.cpp"
(and others). The slider should now work as expected. A simple test
program can be downloaded from

"http://dpartialmirror.sourceforge.net/Test/".

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18897 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775