Fix Matlab viewer for parallel complex vectors

In complex vectors, the output of the Matlab viewer was different
for sequential or parallel vectors. In parallel vectors, there was
a whitespace between the imaginary part and the imaginary unit "i"
hence causing problems when loading in Matlab.
Correctly check input type of Mat argument in MatMPIAIJGetLocalMat

MatMPIAIJGetLocalMat requires MPIAIJ matrix as input, but it used
a explicit cast in the declaration of variables, before checking that
the input Mat is actually of this type.
VecScatterCreateToZero: fix man page

Reported-by: Dave May <dave.mayhem23@gmail.com>
Merge branch 'jose/mat-vec-fixes' into maint

* jose/mat-vec-fixes:
  Correctly check input type of Mat argument in MatMPIAIJGetLocalMat
  Fix Matlab viewer for parallel complex vectors
check for ddot_() in chaco and reject it
print download packages before downloading
DT: remove spurious printing
fixed hdf5.py so that if self.libraries.compression is None the code still runs correctly