Make multiline checkboxes wider in wxMSW to avoid word wrap.

Make multiline checkboxes wider in wxMSW to avoid word wrap.

At least for some versions of Windows (Server 2003 with classic look and feel)
the native checkboxes auto wrapped the label as it wrongly considered that the
width we specified for it was not big enough. Compensate for this by making
the checkbox wider -- this is just a hack but still better than corrupting the
checkbox display.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70015 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775