Improve flexibility of lock file versioning

[erikd]

Currently an existing lock file like example.lock-7.10.2 will only be used by mafia with GHC 7.10.2 and will be ignored by GHC 7.10.3.

I would like to keep the above behavior, but add a fallback wildcard-like behavior so that example.lock-X.Y would be accepted as a valid lock file for any GHC version that matches X.Y.*, but only if an exact match (eg X.Y.Z) is not found.

@tmcgilchrist @nhibberd @charleso Any concerns about this?

[nhibberd]

Nothing comes to mind

[tmcgilchrist]

Nothing I can think of. Is there ever a situation where minor versions need a different version of a package?

My typical practice was to copy the lock file across to match the GHC version I had within the same major version i.e. 7.10.2 -> 7.10.3 and haven't run into any issues doing that.

[erikd]

ghc-prim is one package that can tied to a minor version of that compiler. However, its possible to just leave that out of the lock file and the right thing will happen.