pdfviewer patches from Werner

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73713 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
pdfviewer patches from Werner, Phoenix and doc updates.

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73714 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add pdfviewer unittests, from Werner

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73715 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775