Consider adding LL_REVERSE to utlist.h

[u-u-h]

It's a common paradigm to use LL_PREPEND in a loop and a REVERSE step afterwards to avoid LL_APPEND in list construction. It would be nice to have that built-in in utlist.h

[Quuxplusone]

Yep, makes sense to me. Pull requests welcome; or if not an implementation, at least some sample test cases showing the desired usage would be nice.

Presumably DL_REVERSE and CDL_REVERSE should be added in the same PR.