Standardize option longnames on underscores

Fix #1786
Update changelog with dash to underscore changes

Conflicts:
	ChangeLog.md
Remove option-label entry from script_info

Was used by n3phele, not needed any more
Merge branch 'master' of https://github.com/biocore/qiime into dashes_to_underscores-issue-1786

Conflicts:
	ChangeLog.md
	scripts/denoiser.py
Merge branch 'master' of https://github.com/biocore/qiime into dashes_to_underscores-issue-1786
Fix typo
Merge branch 'master' of https://github.com/biocore/qiime into dashes_to_underscores-issue-1786
Merge pull request #1792 from adamrp/dashes_to_underscores-issue-1786

Changes dashes in option longnames to underscores