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.

Makefile.am

@@ -17,7 +17,7 @@
 
 ALL_RECURSIVE_TARGETS =
 
-SUBDIRS = lib src man po tests gnulib-tests
+SUBDIRS = lib src po tests gnulib-tests
 
 changelog_etc =				\
   ChangeLog-2005			\
@@ -175,3 +175,4 @@ all_programs:
 	@cd ./src && $(MAKE) -s $@
 
 include $(top_srcdir)/doc/local.mk
+include $(top_srcdir)/man/local.mk