Clarify that the range of PETSc versions that work for 0.6 is:  3.3.0 <= version <= 3.4.5.
Implement "-atmosphere one_station" in 0.6.

This atmosphere model reads scalar time-series of the near surface air
temperature and precipitation and uses them at all grid points in the
domain. Resulting climate fields are constant in time *unless* a
modifier such as lapse_rate is used to create spatial variability.

Use "-atmosphere_one_station_file" to specify the name of the file
containing "air_temp" and "precipitation" variables.
Fix ice discharge reporting. Port to 0.6.

We report discharge by keeping track of changes to ice
thickness (corresponds to calving off a whole column of ice) and
Href (corresponds to calving of a fraction of a column). The problem is
that changes in Href *may* also correspond to the advance of the calving
front, which is *not* associated with mass loss.

So, from now on we check if Href increased. If it did, Href's
contribution to ice discharge is zero.
Don't look for TAO if PETSc is recent enough (>= 3.5.0) (in 0.6).
Specify units in a doxygen comment.
Sort out units of the shelf base mass flux.

We need to convert from [kg m-2 s-1] to [m s-1] in a number of places.
Revert "Try to support PETSc 3.5.0."

This reverts commit a8a1a617a284032add7bd8bbf09a75f52e067589.
Try to support PETSc 3.3, 3.4, and 3.5 in PISM 0.6.
Silence CMake 3.0 warnings while supporting older CMake versions.