Check problem when uploading many documents

[turicas]

There is a problem when uploading many documents - if we try to upload, for example, 100 documents, some of these documents are not shown in Web interface (sometimes 3 are lost...but this number changes). No exception is raised in this process.

Should exist a test to verify if the documents were really uploaded.

[turicas]

Probably the best time to fix this bug is when we move to the new PyPLN.Web API that is being developed by @flavioamieiro.
There is a feature on PyPLN.Web that is needed to this check: option to check if a document is in a corpus (or search by document name) or return a list of uploaded documents when documents are uploaded (probably a JSON array with document names, ids and URLs).