Incorrect error handling with Perforce can lead to missing lines added/removed counters for a file revisions

Actual behaviour

Currently when any perforce related error happens when FishEye tries to get p4 describe -dn for a batch of changesets, it fallbacks and tries to get the data for changesets one-by-one.

If this fail, FishEye will try to call p4 describe -s which lists only basic information about changeset and don't provide diff information which is required to calculate lines added and removed for a file revision in changeset.

This result in incorrect lines added/removed counters and potentially can lead to blame calculation errors further in the indexing process

Correct changeset information:

Expected behaviour 

FishEye correctly handles errors which come from Perforce, correctly fallbacks from batch mode and propagates the exception if it can't get the required information from perforce.