Simulate non-semver `>=` using alternations

The original benchmark/test translated all constraints into either inexact or exact Meteor constraints — that is, Rails’s `~>1.2.3`, `>1.2.3`, and `>=1.2.3` became the inexact `1.2.3`, and `=1.2.3` became `=1.2.3` — but also gave all versions of all packages an ECV of 0.0.0, meaning all versions are compatible with each other.

In order to make this test pass without ECV, we need to emulate pure `>=` (without incompatibility between major versions) in some other way.  So, for each constraint of the form `foo@a.b.c` where `foo` has larger major versions available than `a`, we allow those major versions as well.  For example, if we depend on `foo@1.1.11` and the largest version of `foo` is `3.2.0`, we rewrite `1.1.11` to `1.1.11 || 2.0.0 || 3.0.0` in order to emulate a pure `>=1.1.11` with no concern for major version compatibility.