executablePath test: fix file extension treatment
The executablePath test strips the file extension (if any) when comparing the query result with the expected value. This is to handle platforms where GHC adds a file extension to the output program file (e.g. .exe on Windows). Subsequent to the initial check, the file gets deleted (if supported). However, it is the *stripped* filename that is used, which is incorrect. The test currently passes only because Windows does not allow deleting the program while while any process created from it is alive. Make the test program correct in general by using the original (non-stripped) executable filename when deleting the it.