Closes #240. (Port to 0.6.)

Whoever designed Cray's module system must have been worried about job
security. Yuck.
Fix ssa_forward.py. Port to 0.6.
Fix a bug in IceModelVec3Custom. Port to 0.6.
IceModelVec2T does not re-read periodic data. Port to 0.6,

Periodic data is read in once at the beginning of the run (in
IceModelVec2T::init()), so we don't need to check if everything we need
is held in memory (we know that it is).
Fix -ocean ...,cache. Port to 0.6.
Fix -surface ...,cache. See #254. Port to 0.6.
Realized that the User Man should say: Nx and Ny are automatically determined, N = Nx Ny should be composite, and -Nx,-Ny are expert options.  Port to 0.6?
Fix the PDD code in dev. See #254. (Port to 0.6)

The PDD surface mass balance models resets the snow depth once a year,
on the day corresponding to the beginning of the mass balance year. The
code re-setting the snow depth was not designed to work in the case of
non-contiguous updates (i.e. the "cache" modifier). I believe it does
the right thing now.
Minimal fix to #255.

Despite the profound discussion on #255, for now this is the short-term
compromise: if bwat is missing then set to zero (actually: configurable
bootstrap default value).

@ckhroulev:  Code review sought.
Apply the patch provided by Leo van Kampenhout. (Port to 0.6.)
Save CTS when -o_size big is set. See #262. Port to 0.6.
Remove undocumented storglaciaren example from users manual.  Port to 0.6.
The "init. step" of couplers is a method now. Port to 0.6.

Also: re-initialize surface and ocean models at the very end of the
model setup to get rid of side-effects of this step.
Very minor cleanup. Port to 0.6.
Fix snow depth reset code. Port to 0.6.
PDD sub-intervals consistent with interpolation scheme. Port to 0.6.
Initialize variables in PDDMassBalance::step(). Port to 0.6.
-surface_given_period X should take an integer X. Port to 0.6.
Add -timestep_hit_multiples. Port to 0.6.

Also: refactor adaptive time-stepping code and document new adaptive time-stepping decision output. See #259.
Fix a typo in IceModel::step() (in 0.6).