Merge pull request #239 from pwaller/fit

Add rootpy.fit.uncert.correlated_values
extend walk to return classnames and directories
regular expression search in combination with a cache
rename ReSearch -> find; make find_fnc, i.e. search or match, optional
PEP8: return statement should be on a new line
Merge pull request #286 from schmitts/fast_object_search

Proposal for a fast object search with regular expression
Merge pull request #310 from pwaller/legend-improvements

Add .primitives to get the rootpy.root_collections.List of entries
Introduce rootpy.ROOT, a pluggable replacement for `import ROOT`
Add `from __future__ import absolute_import` to all top-level modules