The source project of this merge request has been removed.
jinja2_template.py: Compile the same source only once and use compiled source next time.
compile function takes a lot of time, thus this change saves time when the same source is used many times in apache frontend SR.
@jm Can you review this change? In my apache frontend test environment, with this change, I can save 50 sec to compile the same jinja2 template about 1800 times.