man: build the scdoc based man pages

man: build the scdoc based man pages

Note that scdoc does not handle natively handle the dummy
modules.dep.bin.5 entry, so we need to create one manually.

Not a big deal, since it's single static line anyway.

Also: pkg-config --variable=scdoc scdoc, produces the full executable
and path, although for now we stick with the AC_PATH_PROG approach.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
[ Do not add the stub man page (modules.dep.bin.5) to CLEANFILES
  to avoid removing a file that is tracked by git. Also fix a typo
  s/AM_V_SCDOR_/AM_V_SCDOC_/ to make silent rules to work ]
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>