Attempt to make the test suite work with Windows executables.

The test suite still assumes a POSIX shell to run the tests, but now handles
the case when the executables themselves are (cross-)compiled for Windows,
with a .exe extension. Also, DOS line endings must be converted to UNIX
line endings in some cases.

Some tests now pass on Linux+Wine, but others do not, mainly due to Wine
not handling services very well.