Alsa: Revise the use of the environment variable 'PA_ALSA_PLUGHW' so it correctly influences the Device-List and the capabilities reported.  Also rename a mis-leading variable and add one additional DEBUG line.

git-svn-id: https://subversion.assembla.com/svn/portaudio/portaudio/trunk@1911 0f58301d-fd10-0410-b4af-bbb618454e57