run-tests: pre instantiate pygments objects This speeds up run-tests.py diff output by 10x, which affects developer experience significantly. As demonstrated by the following test: ``` #require pygments $ for i in `seq 1 200`; do > echo ' $ echo '$i >> test-a.t > echo ' wrong' >> test-a.t > done $ cat > walltime.py <<EOF > from __future__ import absolute_import, print_function > import os, sys, time > t1 = time.time() > os.system(' '.join(sys.argv[1:]) + ' >/dev/null 2>/dev/null') > t2 = time.time() > print('%0.2f' % (t2 - t1)) > EOF $ $PYTHON walltime.py $TESTDIR/run-tests.py -l --color=never $TESTTMP/test-a.t 0.24 Before this patch: $ $PYTHON walltime.py $TESTDIR/run-tests.py -l --color=always $TESTTMP/test-a.t 2.46 After this patch: $ $PYTHON walltime.py $TESTDIR/run-tests.py -l --color=always $TESTTMP/test-a.t 0.25 ```