Add __str__ and __add__ to qiime.util.MetadataMap

This will facilitate printing and merging of MetadataMap objects.
Modify merge_mapping_files library code

Removed write_mapping_data (one can now call print or str() on
MetadataMap objects)

Changed merge_mapping_files to make use of the newly added __add__ function
of the MetadataMap class.
Replace tests for new merge_mapping_file code
Fix script to work with new library code
Merge branch 'master' of https://github.com/qiime/qiime into improve_metadata_map

Conflicts:
	qiime/merge_mapping_files.py
	scripts/merge_mapping_files.py
	tests/test_merge_mapping_files.py
Accidentally deleted this file!
Update script interface
Merge branch 'improve_metadata_map' of github.com:adamrp/qiime into improve_metadata_map
Address comments from @jrrideout

Should be good to go, unless there are additional comments
Remove unneeded function import
Modified check_id_map.py to use IUPAC characters from bipy, issue #1421
changing libraries from cogent to unittest
changing assertEqualItems -> assert_almost_equal
changing self.assert_almost_equal -> assert_almost_equal
Fixing tests for align_seqs
Typo

I think the sentence makes more sense with "if" instead of "in".
fixing some of the erros, still 51 scripts to go
use bipy.draw.distributions.boxplots
fixing some of the erros, still 47 scripts to go
fixing some of the erros, still 43 scripts to go