Pa_process: Fix input channel adaption by not skipping the input conversion when the host and user number-of-channels are not equal.  The bug manifested when recording mono from a stereo-only device (eg with Alsa hw: devices on some sound-cards), and was reported by the Mixxx team -see https://bugs.launchpad.net/mixxx/+bug/900364.  (In the long-term, some refactoring may be preferable.)  Also fixed copy-paste typos in comments.

git-svn-id: https://subversion.assembla.com/svn/portaudio@1913 0f58301d-fd10-0410-b4af-bbb618454e57