Canonicalize path util and fix NoTargetsError when proj root symlink

When searching for the primary package, the return from a call
to getCurrentDirectory is compared via (==) equality with a
canonicalised path resulting in an inability to find the primary
package if no targets are specified when the project root is in,
or contains a symlink/junction or, when, under certain conditions,
the capitalisation of the drive letters don't match on Windows.

This breaks cabal functionality in emacs' haskell-mode (at least on
Windows) as it relies on automatic package detection.

With this commit, the test case added in the commit prior now passes.