It turns out there are shockingly few cases of manifestparser manifests that actually use the ';'
character as a comment. Because we will soon allow inline comments, deprecating the use of ';' will
ensure that values are allowed to have semicolons in them.
Even without inline comments, might as well enforce consistency across manifests.
MozReview-Commit-ID: AEPPQFdNXG0
--HG--
extra : rebase_source : 3540fa385f328bffb020c0a6debc4d2b3a90ed39
