Merge branch 'ns/raise-write-index-buffer-size'

Merge branch 'ns/raise-write-index-buffer-size'

Raise the buffer size used when writing the index file out from
(obviously too small) 8kB to (clearly sufficiently large) 128kB.

* ns/raise-write-index-buffer-size:
  read-cache: make the index write buffer size 128K