1. PA uses Vala's "Posix" package (see line 23 of libpulse.vapi).
    These dependencies have to be declared in the *.deps file.

 2. Fix obvious copy/paste error.

 3. Rename the parameter to match the C function. This simplifies
    understanding what this parameter means.

 4. According to the official documentation the "dev" parameter
    for playback/capture streams on connection may be NULL and this
    is the default. Change the method definition accordingly.