* Implement dynamic loading of the Cairo DLL on Windows similar to how it was

* Implement dynamic loading of the Cairo DLL on Windows similar to how it was
  done for GDI+.

* Enable the use of the wxCairoContext on MSW.

* Enable creating a wxGCDC from an exisiting wxGraphicsContext.

* Since it's possible for a DLL that is using wx to not be on the PATH nor in
  the same location as the .exe, change the wxDynamicLibrary::RawLoad method to
  explicitly look first in the same place as the main wx-using binary.  This way
  it will find DLLs that are in the same folder as the wx-using binary even if
  that would not be in the normal DLL search path.

* Change wxDCImpl and wxDC::GetLogicalScale to be const methods.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68935 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775