Restructured TS map computation

As close to final as it could get today.
This is re-setting the `astropy-helpers` git subproject pointer to an older version:
```
$ git show -s --format=%ci 5fd32d0edc34f94de9640fd20865cfe5d605e499
2014-10-22 22:26:11 +0100
$ git show -s --format=%ci 956d39893123b593abe588524ed4490641a8d920
2014-09-04 12:53:43 -0400
```
Did you do this by accident?