Fix tail in from_L_R in gf_generic

The order_max was not set properly.
Fix a missing mask in tail fit (imfreq)

I applied the patch provided by Thomas.

  modified:   pytriqs/gf/local/gf_imfreq.py
install : update boost.rb
Merge pull request #41 from lmessio/master

Changes in the doc and one bug removed in det_manip
Correction: new test det_manip_constructor

The matrix was singular !
(-> exception on OS X).
Fix #42. Conj overload issue

std::conj returns a complex according to std.
On gcc, we need to define it (bug?) but on clang libc++
it is an error.

-> one test is still failing : to be decided later
Fix missing cached key in archives

When an object with __hdf_write__ was written in an archive, the
corresponding key was not cached. Therefore, one could not access
the object which had just been written.
Fix test after conj changes

conj(double) now returns a complex. The mapped_functions test output
had to be fixed accordingly.
gfs. Rm code introduced only for Krylov QMC

- This function was redondant : qmc code cleaned.
- using make_clone in gfs namespace for ADL usage.
mc_tools : add debug print under macro

When TRIQS_MCTOOLS_DEBUG is defined,
the qmc now reports some basic debug info
(when is a move accepted, rejected, ...).
gf: generalize the constructor of gf_mesh from domain

- to add "positive_only" flags, in the case
we need both negative and positive frequencies in matsubara.
pytriqs: add option to use mpi4py instead of boost.python.mpi

- to choose mpi4py over boost.python.mpi, pass -DPython_use_mpi4py=ON

- boost.mpi stays the default for python, but
  adding the possibility of using mpi4py instead.

- Due to numerous pbs on recent OS X + brew installation.
  boost.mpi does not work (crash in openmpi ??), mpi4py does

- the pytriqs/utility/mpi.py is now configured by the cmake (like
  version.py) to prepare one of the two possibilities.

- TODO:  not tested carefully : to be done in other machines.
arrays: fix mapped_function (conj overload)

- conj overload should return complex, as in standard.
- changed the test output for mapped_function.
- fixed make_matrix_view and example in doc.
work on doc for gf, and details.

- little details : code cleaning, clang formatting,  along
with documentation writing for c++ gf.
- separated the mesh in small class for better doc.
- work on documentation : reorganize specialisation, ...
Iteration over the doc

This is an iteration over the doc mainly thank to Priyanka.
I fixed another couple of details on the way.
documentation for tail (python+c++) and for profiling
Add doc for tightbinding and bravaislattice.
gfs: Fixed bug in index_to_point.
gfs: Fix bug in imfreq with <0 freq.

- there was a confusion in gf imfreq, in the new case
where freq can be <0 (non real gf, or for product gf).
- index: is the matsubara n, as in the struct matsubara_freq
  index can be >0 or <0
- linear_index : is the shift from the 0. It is always >0.
  Fixed function to compute it.

- Also changed the construction of mesh_point in the generic iterator.
  Before, was constructed with a mesh point of index 0
  Now, added a new constructor on mesh_point_t, just taking the mesh
  which construct the *first* mesh_point.
  Fixed linear, discrete, product accordingly.
  Added to the documentation of the concepts of gf.
Fix const in apply_on_tuple