Fix #124: ^0.11.0-rc.2 should not match 0.11.0

[dhardy]

This broke a few tests, but my reading of the rules is that these did not match spec:
https://docs.npmjs.com/misc/semver#tilde-ranges-123-12-1

On the other hand whether we want to make this change I don't know:

• The current rules effectively mean 0.11.0-rc.2 < 0.11.0 — that test itself won't pass but the compatibility (^) rule allows people to treat it almost like it is (note though that ^0.11.0 will never match 0.11.0-rc.2 due to restriction on prerelease tags)
• It may be valid to consider effectively x.y.z-A < x.y.z for all x/y/z/A (see my other comment)

[dhardy]

Also CC @alexcrichton who commented on the semver rule (sorry to CC you so much; perhaps you shouldn't have so many talents!)

[steveklabnik]

I believe I'm pro this change. It makes sense, and it's what npm does.

[dhardy]

My apologies, but I do not believe what I did here is correct since semantically pre-release versions come before final versions (i.e. 1.2.3-beta.2 < 1.2.3). This is a confusing thing about semver which isn't stated explicitly in the spec, but I think it only makes sense that way (and some of the examples seem to confirm this). I.e. it should be valid to release 1.0.0-pre.1 and then release 1.0.0 afterwards.