STY: make function_base.py pep8 compatible

This makes function_base.py almost pep8 compatible.
ALSO, removes the Set import which is unneeded since python 2.4,
and organises the import statements.
STY: Error and warning newline standardization in function_base.py

Continueing the pep8 effort, adds newline afer each `Error(`
and tries to wrap correctly.
STY: error and warning formatting on 'function_base.py'
Merge pull request #3775 from jarondl/doc-function_base-pep8

STY: make function_base.py pep8 compatible