Patch for 'normalize' that crashed with empty set

When a function is called on an empty serie, the function 'normalize'
encoutered an error.
Now it raises a custom error that is tracked by the function 'evaluateTokens'
and returns []
adding test function for normalize()
Use url() and import views in URL definitions
Add configurable URL prefix
Handle STATIC_URL with prefix
Resolve all URLs or prefix them with baseUrl
Load future url on Django 1.4
Disable this for now
Properly handle empty prefix
Merge branch 'master' into fix/reverse
Update reverse call to use named URL
Add a lint tox target, fix all import issues
Fix some whitespace issues
add pow() function, convert squareRoot() and invert() to use safePow() instead, refs #803
backport of changed() function to master, refs #530
Merge branch 'master' into new_change_function
make safePow more impervious to math domain errors
wrong var name
Merge pull request #808 from obfuscurity/pow

Add pow() function
adding 'a Unix-like OS' as a requirement