XPG requires insque() and remque() to work with linear lists and not just

XPG requires insque() and remque() to work with linear lists and not just
circular lists.  Amazingly, they managed to extend the requirements to no
longer match the behavior of the VAX instructions they were modeled after,
so the trivial VAX ASM versions have to go.  Nice job breaking it, X/Open!

Based on a diff from enh (at) google.com
ok miod@