The function has two potential users which both managed to get wrong
their implementations (the one in builtin-rm.c one has a memleak, and
builtin-merge-recursive.c scribles over its const argument).
Signed-off-by: Alex Riesen <raa.lkml@gmail.com> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>