The UndoRedoRedlineGuards that SwUndo::{Un,Re}doWithContext wants to
put on the stack aren't actually variables, so the destructor gets
invoked before the function call that the guard is supposed to protect.
Regression from CWS undoapi.

Because the default text encoding in Python 2 is "ascii" these would
throw a UnicodeEncodeError: 'ascii' codec can't encode character...

This helps eliminate dozens of IS_AVAILABLE macros scattered across
Calc code.  I'm sure we have other similar macros like this
elsewhere.

...so that tinderbox output becomes useful.