Remove Blatter stress balance code from dev.

Further development should go in the 'blatter' branch, which is up to
date now.
A bit of cleanup.
Fix a bug in "Timeseries".
Add "climatic_mass_balance_original". Closes #232.
More rational construction of basal strength documentation, but it is still not done.
Edits through end of section 7.1 on modeling basal strength.  Much better.
Remove unused code.
Move the basal sliding law into ShallowStressBalance.

...and remove it from IceModel. Most of the changes are purely cosmetic.
Update stress balance command-line options. See #144.

All tests pass. Now I need to update all the scripts and document new
the new option.

-stress_balance
 {none,prescribed_sliding,sia,ssa,prescribed_sliding+sia,ssa+sia}

Old options that are affected: -no_sia, -sia (not used, I bet),
-ssa_sliding, -ssb_constant (used once).
Update -ssa_sliding option in examples/*.
I think this is satisfactory documentation of the two documented hydrology choices.
Documentation of marine ice sheets and bed deformation in User Manual in pretty good shape.
Update more scripts (-ssa_sliding, -no_sia).
Update stress balance options in the manual.

-stress_balance ssa, -stress_balance ssa+sia instead of -ssa_sliding and
 -no_sia.
Fix a typo in the manual.
Remove last mentions of -no_sia and -ssa_sliding.
Take care of FIXMEs in the init sequence graph.
Fix a typo in a doxygen comment.
Zero-pad years in stdout and -extra_split file names.

This will make it easier to sort PISM's output files. For example,
"ncview ex-*.nc" should do what you expect it to.
Change all executables to use default output name 'unnamed.nc'.

The User Manual does not need to be cluttered with the strange
historical naming scheme.