Fix order-dependent unit tests

Found this issue after testing against scipy 0.9.0.
Use izip instead of zip

per @wasade's request
Minor fixes based on @wasade's review
Handle 0x0, 0xn, and nx0 empty/null special cases

Thanks @wasade for catching this!
Update default biom_config comments

They now reference ScipySparseMat.
Merge pull request #227 from jrrideout/scipy-sparse-backend

Add a scipy-based sparse matrix backend
start of pip setup
Clean up sparse backend type reporting

The discrepancy in sparse backend type reporting between CSMat and ScipySparseMat occurred because CSMat was an old-style class and ScipySparseMat is new-style (inherits from object). This caused the formatting of the class name to differ. CSMat is now a new-style class.

The new output for both backends looks like:

     SparseObj type: CSMat
     SparseObj type: ScipySparseMat

This is a bit cleaner/clearer than what we had before (e.g., biom.backends.csmat.CSMat), since users are really only concerned with the name of the backend. The backend name output by ``biom show-install-info`` is now consistent with the name users must add to their BIOM config file.

Fixes #231.
Merge pull request #232 from jrrideout/issue-231

Clean up sparse backend type reporting
add metadata support for CommandOut
specifying output right...
table converter now supports CommandOut
show install info and table subsetter using CommandOut
more commands up to speed

cleaned up table summarizer some and compute_counts_per_sample_stats
validate table now up to speed
Add python-code/ removal mention to ChangeLog.md

Fixes #239.
Merge pull request #240 from jrrideout/issue-239

Add python-code/ removal mention to ChangeLog.md
empty lists to table_factory are no longer allowed

* not addressing for dense as it is being dropped
* raises TableException if [] is passed in as data
removed comments
added Table.nonzeroCounts
* counts over axes
* can be optimized much further for sparse matrices
* did not test for dense as we are dropping support