move git sha/tag column to end of description

If the git description for the release's hash is not already included in the release's description (and thus isn't just a hash), append it to the end of the description when we display it.

Here's how it looks:

```
➜  hk releases -a hkdist        
v120  b  Jan 22 15:59  Deploy 15146e5
v121  b  Jan 22 16:03  Deploy c11e447
v122  b  Jan 22 16:56  Deploy e236e1b
v123  b  Jan 23 11:47  Deploy 71316e5 (v20140123~5)
v124  b  Jan 23 14:56  Deploy 8089f65 (v20140123~2)
...
v136  b  Feb 11 14:55  Removed IMPORTANT config vars.
v137  b  Feb 25 12:16  Deploy db8dba2 (v20140225)
v138  b  Mar  3 12:45  Attach HEROKU_POSTGRESQL_ORANGE resource
v139  b  Mar  3 12:50  Detach HEROKU_POSTGRESQL_ORANGE resource
v140  b  Mar 11 21:01  Deploy dff5cef (v20140311)
```

Fixes #93. /cc @raul @kr