Update conf.py

Added path normalization and home directory expansion.
Update conf.py

Added creation of PID_DIR in case the pidfile is not found and the PID_DIR doesn´t exist. Under normal circumstances, it should only execute on the first run of carbon.
Update conf.py

fixed path
Update conf.py

Fix indentation
Correct syntax for STORAGE_DIR expansion.

Correct syntax for STORAGE_DIR expansion.
Merge pull request #112 from MATERROR/master

Fixes to conf.py to support path expansion and normalization (eg: PID_DIR = ~/graphite/)