r3733: More build system fixes/features:

r3733: More build system fixes/features:
 - Use .mk files directly (no need for a SMB_*_MK() macro when adding a new SUBSYSTEM, MODULE or BINARY). This allows addition of new modules and subsystems without running configure
 - Add support for generating .dot files with the Samba4 dependency tree (as used by the graphviz and springgraph utilities)
(This used to be commit 64826da834e26ee0488674e27a0eae36491ee179)