added failing test

to help debug issue #7
added test of passing an alternative finder function

this shows how to handle the issue #7 use case with no changes to the MinimalFastaParser code. I don't think issue warrants an code change, but since I wrote this test it doesn't hurt to add it to PyCogent.
can now use PyCogent within the IPython notebook

[FIXED] trap stream IOErrors that arise in IPython notebook

--HG--
extra : rebase_source : 66b156b11ab8678306047dced17b06245baee7cf
Closes #43
Merge pull request #49 from gregcaporaso/issue-43

removed dead link
Merge pull request #8 from gregcaporaso/issue-7

added a test while investigating issue #7
Merge pull request #42 from jonatanfan/master

Subtracted 18 (hydrate) from all ProteinWeights as this is already added...