fastannotate: record some TODO items from indygreg's review
Some of these I'll address more or less right away, but some will take
a while for us to resolve.
Differential Revision: https://phab.mercurial-scm.org/D4200
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL