kbuild: Add 'make namespacecheck'

kbuild: Add 'make namespacecheck'

make namespacecheck lists globally visible symbols that are not used
outside the file that defines them.  These symbols are candidates for
static declarations.  It also lists multiply defined symbols.
namespace.pl knows about lots of special cases in the kernel code,
including exported symbols and conglomerate objects.

The patch also corrects the usage of scripts/reference*.pl, they need
$(src).

Signed-off-by: Keith Owens <kaos@ocs.com.au>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Index: 2.6.9-rc1/Makefile
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