debian/rules bug fix: the RGL was not included in .deb packages

The problem was that the RGL was both built and copied to the destdir
during the build step, which caused it to be deleted before the install
step. It is now copied to destdir during the install step.

debian/changelog

@@ -1,3 +1,9 @@
+gf (3.10-2) xenial bionic cosmic; urgency=low
+
+  * GF 3.10
+
+ -- Thomas Hallgren <hallgren@chalmers.se>  Fri,  5 Mar 2019 16:00:00 +0100
+
 gf (3.10-1) xenial bionic cosmic; urgency=low
 
   * GF 3.10