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
Documentation fix
Documentation fix
documentation fix
Merge pull request #1412 from heatyen/info

Documentation fix
remove dependency on cogent.PROTEIN
Merge branch 'master' of github.com:qiime/qiime into remove-protein
modified to use bipy.core.sequence.DNA
modified to use bipy.core.sequence.DNA
modified to use bipy.core.sequence.DNA
modified to use bipy.core.sequence.DNA