make sure that sub-grid interp. of basal melt also is applied in cold mode
rewrote sub-grid gl interpolation --> now only direct assignment of array elements, e.g. it is written to gl_mask(i,j) but not gl_mask(i+1,j), works
avoid seldomly occuring negative values, clean up
Merge branch 'pikdev_pgg' into pik

this is pgg as in branch part_grid_global, that has been ported to PISMs
dev branch.
meltrate increase per K as option.
fit meltrate increase per depth with exp function.
corrections and cleanup.
Merge branch 'pikdev_meltadjust' into pik

Basal meltrates from ocean models are adjusted to the evolving
ice geometry. The adjustment is derived from the 3eqn melt parametrization
as in Hellmer and Jacobs 1998.
kill unattached partial grid cells

otherwise ice can be stored in partial grid cells in the middle
of the ocean and be accessed later when the ice front
arrives there again. we do not want that.
allow free boundaries in regional setups

bcflag values > 1 allow the sia flux to alter ice thickness at the boundaries.
bcflag == 1 handles the standard case as before.