Defensive approach in the pass manager when apply() on unknown pass type

I still don't know if we should raise or warn or whatever here. At least
do not call blindly display() unless there is a super-class for passes
that provide it.
Defensive programmign apart, code is more readable with the check for
'Analysis' type. Still wonder if "transformation" is the right name
for the pass.
Improve comments in syntax module (Pythran Syntax Checker)