process.compile_precip wasn't rebuilding when the folder dependency changed

[jordansread]

Careful on this one ... May need to investigate this to make sure it is behaving as expected. I added an unlink to the tars in fetch.precip that were old (and no longer in the time range we are using), and this target didn't change after make.

[dblodgett-usgs]

When I run in debug, I get warnings about the mimetype / adding a reader.

In as.reader(v) :
  Could not find specific readData method for viz.id=precip-shapefiles, mimetype=text/directory; returning filepath. Specify reader to override.

It appears I get the same error for every one of the tar files in the output folder... (more than 50 of the same warning).

[aappling-usgs]

Folder dependencies are really tough. It's possible we'll get more mileage using an indicator file within that folder, or maybe we need to be matching up timestamps for every file....