Fix memstats in renumber_positions(). Fixes #10

Added some calls to register_allocation in the subroutine renumber_positions
in the file Fields_Manipulation.F90. This is to prevent incorrect memory
stats at the end of a calculation.
This is a minor bug fix for the build framework. The Make.dependencies is not in sync with the code and thus causes make makefiles
to fail.
Allowing users to specify which multimaterial mean to use in the bulk_viscosity algorithm.

This has been implemented more generally so that all multimaterial averaging routines are capable of it regardless of rank but
nothing other than bulk_viscosity actually exposes the functionality.

A (very) short test has been added.
Merge branch 'master' into fluidity-core/lift-velocity-bcs