Specify >= or <= for vcs requirements.

[mforbes]

It would be useful to be able to specify >= or <= requirements for version controlled requirements. For example

hg+http://bitbucket.org/mforbes/pymmf>=633be89a#egg=pymmf

The idea would be that any revision that is a descendant of the specified revision would be acceptable. One could also specify <= to mean any parent would satisfy the requirement (though I don't really have a use-case for this). I suspect that one would always have to specify "=" so that a revision can be found. (If one specified ">", then there is in general no unique way of determining which requirement to pull.)

I took a stab at implementing this, but it looks like vcs requirements do not go through a satisfy check, so I am not sure where I should hook in. Suggestions would be appreciated.

[dstufft]

Closing this, while it may be possible to implement I believe it is a bit of an antipattern and it does not appear that the demand is there to warrant it.