If cabal.sandbox.config contains a "package-db:" declaration with the
wrong path and only the ghc version is wrong, for example:
```
package-db: <DIR>/.cabal-sandbox/x86_64-linux-ghc-7.8.3-packages.conf.d
```
Even though the user is using 7.10.0.20141222 `cabal repl` will correct
this and pass
```
-package-db <DIR>/.cabal-sandbox/x86_64-linux-ghc-7.10.0.20141222-packages.conf.d
```
to ghci, so obviously Cabal/cabal-install is doing some magic.
Conflicts:
Language/Haskell/GhcMod/PathsAndFiles.hs
