Remove duplicate code in PBLingleClark.

We can use IceModelVec2S methods to transfer to/from processor 0.
Remove duplicate code in IcebergRemover.

We can use IceModelVec2S methods to transfer to/from processor 0.
Remove IceModelVec2S::view_matlab().

MATLAB can read NetCDF files, so there is no reason to use ASCII.
SSA::m_velocity_old -> SSAFD::m_velocity_old.

m_velocity_old is used to re-start Picard iterations. SSAFEM does not
use it.
Add an assertion (PISMRoutingHydrology::V has to have ghosts).
Use a "global" Vec in SIAFD_topgsmooth::compute().

(This way it can be written to a file without making copy.)
Simplify IceModelVec::update_ghosts(destination)

The IceModelVec "destination" should be ghosted.
Add comments to benign uses of IceModelVec::copy_to_vec()
Basal heat flux does not need to be ghosted.
v.get_stencil_width() == 0 if v has no ghosts.
thksmooth and schoofs_theta diagnostics don't need ghosts.
Cleanup.
Add IceModelVec::get_dm()

Some PETSc calls (such as DMDAGlobalToNaturalBegin(DM da, Vec
g,InsertMode mode,Vec l)) require that arguments "Vec g" and "Vec l" use
the same DM, or maybe at least that "DM da" was the one used to create
"Vec l". This IceModelVec method makes it easier to ensure this holds.
Commit ff45421 broke IcebergRemover. This should fix it.
Fix a typo introduced in 6f1fe04.

(V does not need ghosts, W does.)
Updated funding sources in README. Port to 0.6.
Added missing character
Use IceModelVec2V to store solution and RHS in SSAFD.
Require PETSc 3.5 for TAO-based inversion tools.
Rewrite put_on_proc0/get_from_proc0 IceModelVec2S methods.

Also add IceModelVec2S::allocate_proc0_copy(), which allocates scatters
and work space the first time it is called for a given DM and re-uses
them for all IceModelVec2Ss using this DM.

To transfer a 2D field to processor 0 and back, do this:

IceModelVec2S field;
Vec field_p0;

field.create(...);
field.allocate_proc0_copy(field_p0);
field.put_on_proc0(field_p0);
// do work on processor 0
field.get_from_proc0(field_p0);
VecDestroy(&field_p0);