Honour --htmldir option to configure script.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
Make sure checkprograms are built as part of 'make test-tarball'.
Do not use old variable INCLUDES and use modern AM_INIT_AUTOMAKE invocation.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>