MB-8029 Make view file sorter use new file sorter module

The view file sorter module now uses the new file_sorter.c
module instead of the module mergesort.c.

Change-Id: I8f289c09452c3f712a859237f6595e27323e20f2
Reviewed-on: http://review.couchbase.org/26190
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>