update_references.sh script

[edulix]

Part of the output when there's a compiler error is something like this:

The actual stderr differed from the expected stderr.
Actual stderr saved to /tmp/compiletestmAAI3R/include_not_found_text_clauses/include_not_found_text_clauses.stderr
To update references, run this command from build directory:
tests/ui/update-references.sh '/tmp/compiletestmAAI3R' 'include_not_found_text_clauses/include_not_found_text_clauses.rs'

But that script doesn't work. If you try to execute it, it fails:

$ tests/ui/update-references.sh '/tmp/compiletestmAAI3R' 'include_not_found_text_clauses/include_not_found_text_clauses.rs'
bash: tests/ui/update-references.sh: No such file or directory

It would be very handy if there was an easy way to update references in specific or in all the unit tests. It can get very tedious doing it by hand.