Make zinc analysis files portable.

We now rebase all the paths in a zinc analysis file to placeholders,
and rebase them back as needed. This allows us to port these files
between systems (e.g., via an artifact cache).
Remove superfluous comment.

Damn you cut-n-paste.
Merge pull request #114 from foursquare/zinc_rebasing2

Make zinc analysis files portable.
combine redundant Address.reference and .pretty

.pretty optionally allowed abbreviated ':target_name'
references to targets in the same BUILD file.
Merge pull request #117 from ryan-williams/address.reference

combine redundant Address.reference and .pretty