use GDAL vsipreload trick to be able to use the vsifile api for all files

this pull request relates to issue http://hub.qgis.org/issues/10124

See the issue for more details and a test file.  This commit adds the feature to debian builds but some issues remain

- where to put the vsipreload.cpp file, in core/ or in providers/?  similarly which debian package this goes into?
- how to enable this automatically for other linux systems and when doing a simple "make install"
- small packaging issue in debian, the .so file does not have the package version number