Added stats and summary functions for trace
calc_interval now throws ValueError when there are insufficient elements.
Bugfixes to stats calculation
Created utilities.py to keep utility functions
Added autocorrelation and autocovariance functions to utilities.
Refactored summary to eliminate stats call
Added stats and summary functions for trace
calc_interval now throws ValueError when there are insufficient elements.
Bugfixes to stats calculation
Created utilities.py to keep utility functions
Added autocorrelation and autocovariance functions to utilities.
Refactored summary to eliminate stats call
Generalizing stats functions; starting to add tests
Added tests for stats
Merge branch 'utils' of github.com:pymc-devs/pymc into utils

Conflicts:
	pymc/trace.py
Minor bugfix in trace.py
Merge pull request #239 from pymc-devs/utils

Added stats and summary functions for trace