namei.h: move "struct componentname" definition outside "struct nameidata",

namei.h: move "struct componentname" definition outside "struct nameidata",
	and provide a valid STDC/C++ definition for function NDINIT

queue.h libkern.h: put explicit casts from void * in insque, remque and memset

(for the records, these changes are necessary to let the files
compile with g++, which is used to build a FreeBSD module
for "Click" -- see www.pdos.lcs.mit.edu/click/ .
Given that they have zero impact on our code, it is worthwhile
to have them in.

MFC after: 3 days