If we're bumping the formula's stable version, then we also must reset
the formula revision to zero.
Note that if and only if a revision is being removed, this commit will
enforce the convention that there should be a blank line before a simple
head spec if and only if there is a formula revision. Any preexisting
violation of the convention (in particular, a blank line before a simple
head spec in the absence of a formula revision) won't be proactively
corrected since we'd not be removing a formula revision in that case.
Closes#369.
Signed-off-by: ilovezfs <ilovezfs@icloud.com>
96cbce015e