Catch IOErrors around opening *.pth files

There was a broken *.pth symlink on one machine.
Less drastic warnings at runtime on invalid sites
Bash completions for dev wrapper
Fix bash completions
Prompt to create vent if none found
Add 'sitelogging/' from commit '45f2a45d7760598c9375ed69d0904531d07977be'

git-subtree-dir: sitelogging
git-subtree-mainline: 08149b29df0904bc50317f6adc3c088e48bf2aa8
git-subtree-split: 45f2a45d7760598c9375ed69d0904531d07977be
Merge sitelogging back into sitetools