Use Sharness as our shell test framework, version 2

This builds on the previous pull-request #201 (Use Sharness as our shell test framework).
This adds a Makefile and a script to aggregate the results from all the test scripts.

The first two commits are the same as in the previous pull-request #201, so no need to merge the previous if you merge this one.
this (and also just `make`) will fail if there is no `test-results` directory. maybe:
```
	-rm -r test-results
```