merge-ort: add pool_alloc, pool_calloc, and pool_strndup wrappers
Make the code more flexible so that it can handle both being run with or
without a memory pool by adding utility functions which will either call
xmalloc, xcalloc, xstrndup
or
mem_pool_alloc, mem_pool_calloc, mem_pool_strndup
depending on whether we have a non-NULL memory pool. A subsequent
commit will make use of these.
(We will actually be dropping these functions soon and just assuming we
always have a memory pool, but the flexibility was very useful during
development of merge-ort so I want to be able to restore it if needed.)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>