Merge branch 'jm/mem-pool'

An reusable "memory pool" implementation has been extracted from
fast-import.c, which in turn has become the first user of the
mem-pool API.

* jm/mem-pool:
mem-pool: move reusable parts of memory pool into its own file
fast-import: introduce mem_pool type
fast-import: rename mem_pool type to mp_block

diff --cc Makefile
Simple merge

diff --cc fast-import.c
index 99f8f56e8c4fbd20b6e6186e26d89eda1baff0d0,ba0cb4bdfb69c3127058a3b923c94f1ea613508b..05d1079d2380694eb53570ede6eaaed97fc4c8e0
--- 1/fast-import.c
--- 2/fast-import.c
+++ b/fast-import.c
@@@ -169,7 -168,7 +169,8 @@@ Format of STDIN stream
  #include "dir.h"
  #include "run-command.h"
  #include "packfile.h"
 +#include "object-store.h"
+ #include "mem-pool.h"
  
  #define PACK_ID_BITS 16
  #define MAX_PACK_ID ((1<<PACK_ID_BITS)-1)