[PATCH] sparsemem base: teach discontig about sparse ranges

discontig.c has some assumptions that mem_map[]s inside of a node are
contiguous.  Teach it to make sure that each region that it's bringing online
is actually made up of valid ranges of ram.

Written-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>