1.9.12 Fix smelt bug with single-OTU data

CHANGES IN VERSION 1.9.12
-------------------------

BUG FIXES

	- `psmelt` function now properly handles single-OTU data

	- Related to https://github.com/joey711/phyloseq/issues/338

	- Builds on https://github.com/joey711/phyloseq/pull/373
Merge branch 'pr/373-honest'