Interactive mode fails to load files on windows

The project has a cabal file. From the command line cabal build works fine. When loading a file in `ghci` however C-c C-l the process fails with the following messages recorded in `*Messages*` buffer:

```
error in process filter: haskell-process-send-string: Writing to process: invalid argument, p4
error in process filter: Writing to process: invalid argument, p4
The Haskell process `p4' has died. Restart? (y, n, l: show process log) y
The Haskell process `p4' has died. Restart? (y, n, l: show process log) l
```

The name of the cabal file is `p4.cabal`.

Reproduce the failure on Windows with the p4.cabal project: run cabal build, then use ghci and C-c C-l in interactive mode. Inspect the *Messages* buffer and the process log, and confirm that loading a file no longer causes the p4 Haskell process to die.

Written by the indexing model from the issue text.