Instead of `E \mid F`, whose size does not depend on the size of its
argument, use `\left. E \middle| \right.`.
Suggested by Alexandre Duret-Lutz.

* vcsn/core/rat/printer.hh, vcsn/core/rat/printer.hxx: here.

* tests/bin/test.py: Always print the expected/effective paragraphs.
Even if they are redundant for single line changes, they enable the
use of update-tests.

* tests/python/transducer.py: Update expectations.