Bug: Without extension file cannot be recognized

[cblp]

$ head -n 1 ./test
#!/usr/bin/env runhaskell
$ ghc-mod check ./test
ghc-mod: target ‘./test’ is not a module name or a source file

ghc-mod version 5.2.1.2 compiled by GHC 7.8.4

[DanielG]

This is tricky since that error is coming from the GHC API I believe. But it's probably just related to guessTarget.

[DanielG]

See also #688