Ignore errors when deleting the executable during testing.

There was already an exception block that was ignoring IOErrors in sub_test
when trying to unlink the executable. Update the except block to also catch
OSErrors.
Use lsof/handle to debug the "Device or resource busy" issues on cygwin32.
Merge pull request #1074 from thomasvandoren/cygwin32-debugging

Robustify sub_test when os errors occur during unlinking.

Ignore errors when deleting the executable during testing.
There was already an exception block that was ignoring IOErrors in sub_test
when trying to unlink the executable. Update the except block to also catch
OSErrors.

Also add lsof/handle call when "Device or resource busy" error occurs. This
will help debug the core issue that is now swept under the covers (see
above paragraph).