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.