scl/Makefile.am: Install SCL files to the correct path

When the build system was changed to a non-recursive form, SCL
installation broke, and an extra scl/ directory got prepended to the
path. This is now corrected.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
Mk/Makefile.am: Include all the files in the distribution

Signed-off-by: Gergely Nagy <algernon@balabit.hu>