Add args argument to REPLWrapper & spawn() to mimic pty_spawn

[tikuma-lsuhsc]

This PR originates from the issue related to my recent PR to octave_kernel [Re: space in the octave executable path in Windows].

This PR contains two commits:

e800dca: This commit adds args list argument to the REPLWrapper constructor so it can be passed down to spawn. A test method has also been added to test_replwrap.py.

303f2fd: pty_spawn and non-pty_spawn codepaths currently handles command and args differently. This commit makes the non-pty path to be comparable to the pty_spawn implementation. That is, command is only split only if args is not provided.

These two mechanisms are essential to allow an octave executable path with spaces to run in Windows. If this PR is accepted, I will create another PR in octave_kernel to finish resolving the issue.

Thanks