display/disp/pretty: better newline handling
comment header updates
evalpy: give stored values a more unique name

evalpy records the original values to see if it needs to assign them
Fix (I think) Bug #26, allow % in python code

Basically, stop sprintf'ing everywhere (well, the various IPC code might still do this, but I don't feel like digging, good enough for now)
and now mod can use % :)
Note test failure on old Octave, rephrase a warning, and comments update
refactor display code and add custom empty sym display