d/p/gdcm-3-fallback-detection.patch: New patch

This patch changes the src/configure.ac file, which forces the
autoreconfiguration of the package.  For that to work, file
debian/autoreconf has been added, as well ass adjustments to
.gitignore and d/s/options.

Closes: #945976
Thanks: Peter Green, for reporting the bug, and Gianfranco Costamagna, for indicating the patch