Fix some compiler nags
Can copy SampleBuffers with different channel count

Also add a new method to expand or shrink a SampleBuffer. Should be useful
when handling mono->stereo (or multichannel) conversions.
Make channel count and blocksize unsigned
Fix typo in method name
Resize buffers based on plugin I/O count

Should help to fix plugins like Independence which declare >2 channels (and
don't support setting speaker arrangement, pffft), however memory corruption
is still present. Not sure what the problem is. =/