build: don't use recursive make to build the 'man' subdirectory

build: don't use recursive make to build the 'man' subdirectory

* Makefile.am: Include 'man/local.mk'.
(SUBDIRS): Remove 'man'.
* configure.ac ($MAN): Adjust so that each of its entries has a leading
'man/' component.
(AC_CONFIG_FILES): Remove 'man/Makefile'.
* man/Makefile.am: Rename ...
* man/local.mk: ... like this.  With further adjustments: each 'foo.1'
target renamed like 'man/foo.1', each '../src/foo.c' dependency as
'src/foo.c', and each '$(srcdir)' usage as '$(srcdir)/man'.  Also ...
(mandep): Adjust, removing the leading '../' component.
Several whitespace adjustments while at it.
(ASSORT): Remove, it's already defined in the top-level Makefile.am.
* cfg.mk (sc_option_desc_uppercase, sc_man_file_correlation): Remove
the associated recipes, they are now directly available from the
included 'man/local.mk'.  Actually, the other changes in this commit
have made these recipes instable and not completely correct, but that
will be fixed in later changes.