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.
taking triqs/utility/c14.hpp from 1.2-dev
added mpi files from 1.2-dev
Exposed MeshImFreq. Added field start_at_0 in ALL cases in hdf_write of mesh matsubara_freq. Otherwise, not same interface for case positive_only/not positive_only.
Remove normalization from Hilbert trafo
added explicit cast of statistic in h5_write of legendre and matsubara