Fixed wrong minus sign in FT definition.
Merge pull request #79 from tayral/fix_doc_ft

Fixed wrong minus sign in FT definition.
gf: fix triqs_auto_assign for gf_view Backport from 1.2
backport from 1.2(mpi). Minor add in array

- added a is_special trait in array assignment
  used in later development. No change here.
- backported at Thomas' request.
fix mpi/vector, added test
added first draft of MPI documentation
Merge branch 'mpi' of github.com:TRIQS/triqs into mpi