bundle: add a applybundle1() method
This is one step towards removing a bunch of "if isinstance(gen,
unbundle20)" by treating bundle1 and bundle2 more similarly.
The name may sounds ironic for a method in the bundle2 module, but I
didn't think it was worth it yet to create a new 'bundle' module that
depends on the 'bundle2' module. Besides, we'll inline the method
again later.
#require docutils gettext
$ $TESTDIR/check-gendoc zh_CN
checking for parse errors