Merge topic branch t/build into pu

Merge topic branch t/build into pu

* The build is quiet by default, use V=1 to get old behaviour.
* Create compressed man page (dss.1.gz).
* dss -V now shows the git version.

* refs/heads/t/build:
  build: Compress the man page.
  Avoid rebuilds of lopsub-generated files.
  build: Use variables for lobsubgen and rm commands.
  Make the build quiet by default.
  build: Create dependencies on the fly and implement dynamic versioning