Build fixes for VC8, compiler warnings fixed, and some minor wxDC zoom changes.

* Added modified version of FindwxWidgets.cmake to prevent manifest build and link errors
  with VC8.
* Fixed ambiguous math function ( sqrt, atan, cos, etc. ) call errors when building
  with MSVC.
* Moved bitmap copy bitmap source file destination to the build path to prevent source
  tree pollution and library rebuilds when building on different platforms.