geo, source:

Renamed `CharacteristicSource` to `CharacteristicFaultSource`.
tests/source/characteristic_test:

Renamed `CharacteristicSource` to `CharacteristicFaultSource`.
source/characteristic:

Minor pep8 fix.
tests/sources/characteristic_test:

Minor pep8 fix.
Merge pull request #110 from larsbutler/char-fault-source

Rename CharacteristicSource to CharacteristicFaultSource

[r=trivial]