#31 allow --copy-via=none when Shared != Local

[Aaron Darling]

Right now --copy-via=none only works when Shared ==
Local.
If the database is pre-distributed, it may be desirable to
have --copy-via=none to force mpiblast to use the
pre-distributed database and balance load solely via
query segmentation and not via db segmentation.

When copy-via=none, some sanity checking should be
performed to make sure that all fragments are accessible
to workers in some form.