Clean tests

Great scripts to test stuff; most come from unpublished scripts from our Jenkins instance.
A lot of cleaning in the tests/sav directory.
And some unpublished tests

The `search_tests.sh` script is quite useful to retrieve the original program for some test:
~~~.sh
$ ./search_tests.sh hello_world sav/base_var_type_evolution_null_alt3.res
../examples/hello_world.nit
base_var_type_evolution_null.nit
~~~

It will be also used by Jenkins to check that each sav/*res file has a corresponding test; since commit 'tests: add missing test files whose sav files where committed' show that sometime the .res are committed but without the corresponding .nit

The `search_tests_git.sh` looks in the git commit to found modified things to tests.
Basically, the simple usage is to perform all engines on the result:

~~~.sh
$ ./testall.sh `./search_tests_git.sh origin/master HEAD`
~~~