Merge branch 'tb/midx-write'

Code clean-up by splitting code responsible for writing midx files
into its own file.

* tb/midx-write:
  midx-write.c: use `--stdin-packs` when repacking
  midx-write.c: check count of packs to repack after grouping
  midx-write.c: factor out common want_included_pack() routine
  midx-write: move writing-related functions from midx.c

Author: gitster

Makefile

@@ -1075,6 +1075,7 @@ LIB_OBJS += merge-ort-wrappers.o
 LIB_OBJS += merge-recursive.o
 LIB_OBJS += merge.o
 LIB_OBJS += midx.o
+LIB_OBJS += midx-write.o
 LIB_OBJS += name-hash.o
 LIB_OBJS += negotiator/default.o
 LIB_OBJS += negotiator/noop.o