Fix wavplay on linux, and maybe OSX

[contradict]

This change fixes the wavplay method on Linux, I don't have an OS X machine to test but it might work there too.

[coveralls]

Coverage increased (+0.2%) to 67.245% when pulling 4e08611 on contradict:update-wavplay into b6a1b7f on dancasimiro:master.

[dancasimiro]

Are the OS checks strictly required? I wonder if it would be more flexible to simply check for presence of the libraries. That might make it work on other operating systems, such as windows.

[contradict]

I was following the advice here for dealing with OS differences.

It looks like there is a preview of PulseAudio for windows and maybe even a way to get it working on OSX, so this might work. I don't have a Windows machine to test with either, so I have no way to test this approach.

If it did work, it seems that PulseAudio is not the first choice for audio on either of these platforms, so testing for the libraries would still need an OS-dependent search order. I think splitting by OS first and then searching for a library that works is a more practical strategy than looking for a library that works everywhere. This also splits the maintenance to people who are proficient with each platform (or even have an example to test).

[dancasimiro]

I think that the library checks are sufficient and that the OS checks are superfluous. However, this is a step in the right direction and I will merge as is.