Bugfix for rust-lang/cargo#3202

[steveklabnik]

We improperly assumed that if we had a wildcard patch version, we must
have a non-wildcard minor version. This is actually incorrect.

[steveklabnik]

While this fixes the panic, it exposes another bug:

[steve@becoming cargo (master)]$ cargo build
    Updating git repository `file:///home/steve/src/semver`
   Compiling semver v0.5.0 (file:///home/steve/src/semver?branch=cargo3202#2719cb6d)
   Compiling cargo v0.14.0 (file:///home/steve/src/cargo)
    Finished debug [unoptimized + debuginfo] target(s) in 47.90 secs
[steve@becoming cargo (master)]$ cd ~/src/foo
[steve@becoming foo (master)]$ ~/src/cargo/target/debug/cargo build
    Updating registry `https://github.com/rust-lang/crates.io-index`
error: no matching package named `semver` found (required by `foo`)
location searched: registry https://github.com/rust-lang/crates.io-index
version required: 0.*.*
versions found: 0.5.0, 0.4.1, 0.4.0, ...

[steveklabnik]

I am confused as to why this fix works; that is, the logic is clearly wrong, but these lines were identical in v0.2.3.

and indeed this test fails:

---- version_req::test::test_cargo3202 stdout ----
    matches: Predicate { op: Wildcard(Patch), major: 0, minor: None, patch: None, pre: [] }, Version { major: 0, minor: 5, patch: 0, pre: [], build: [] }
thread 'version_req::test::test_cargo3202' panicked at 'did not match 0.5.0', src/version_req.rs:515

so why did it actually work before?