Rather than regex the output of `git show <rev>:<path>`, we write the
output of `git cat-file blog <rev>:<path>` to a temporary file, and then
operate on it just as we would a normal formula.
I haven't observed any speed difference. `git cat-file blob` is faster
than `git show`, but the "slow part" is still the git-rev-list
invocation. But really it's pretty fast overall.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
The output happens as it is determined, rather than all at once, which is preferable for CLI commands. This meant I had to hard-code the left-justification.
The pre-amble warning is removed. Instead the command outputs the git checkout command for each she that you can type to get that old formula.
I decided that reseting the one file will work 99% of the time and that it is too risky to reset the whole repo, this will roll-back bug fixes. Instead we should add functionality to compat/ in order to support old formula as required. Sometimes deps may have to be rolled-back too, but the user will have to figure this out on an ad-hoc basis. We are assuming a failure sophisticated user anyway, one who would like to get old versions of stuff.
I moved most of the functions into Formula since IMO this makes more conceptual sense.
I made the she get abbreviated by git (using --abbrev-commit) itself so it as short as can be.
