[schema] Make syntax compatible with print_function
yams seems to exec() us sometimes (instead of __import__()), and
yams.reader uses print_function nowadays.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html