Merge pull request #1 from hagberg/thenovices-pagerank

Rework dangling nodes and personlization approach
Minor fixes; Fix bug in scipy routine
Always use 'N' for the number of nodes
Fix pep8 errors
Having dangling vector default to the personalization vector
Avoid dict comprehension to support Python 2.5
Clean up the power iteration loop slightly
Switch from xrange to range for Python 3 support

Obviously range() is not ideal for Python 2, but usually max_iter will be
small enough that it shouldn't be a problem. If needed itertools.repeat can be
used.
Change two more xrange to range
Add import guard for scipy in tests
Add numpy guard to tests
Fix a typo
Add more numpy guards, since the original import guard was removed
Move tests around to properly skip tests that need NumPy and SciPy
Remove ImportError
Update copyright, attribution
Add not_implemented_for multigraph check
Use G.nodes() ordering in pagerank_numpy