Add missing .cmake scripts.
Update a directory name in FindPISM.cmake.
Adjust to recent changes in PISM.
Fix surface mass balance units.
Remove unused code.
Remove "sprintf" (one should never use sprintf).

Use snprintf if you have to.
Remove headers from CMakeLists.txt.
Clean up PSConstantGLINT2.{c,h}pp
desm silently segfaults if an output directory is absent.

Added assert statements that call abort() right after it fails to open
the file.
Revert "Remove headers from CMakeLists.txt." (sort of).

This reverts commit 25172c72ae9cc494d12b887c6429778b10e36a84.