Remove it from the suggested development ./configure line

Reviewed-by: iustinp

This adds a simple diagram for the cluster architecture and also adds a
dependency on graphviz (both doc and in configure).

Reviewed-by: imsnah

Reviewed-by: iustinp

Reviewed-by: ultrotter

As a nice side-effect this also fixes "make distcheck".

The way used to include the generated rapi-resources.sgml file only
works if it's built in the same directory. That's not the case during
"make distcheck". The patch changes the sed script used for variables
to include the file using its absolute path.

Reviewed-by: iustinp

Reviewed-by: iustinp