Stray 'l'

One of the ells brought a friend. I told the friend to go away!
Merge pull request #1 from dsheets/patch-1

Stray 'l'
Use the past perfect (with implied "were") for tests that have been run
Save backtraces for errors if they are available
Don't spam the terminal with backtraces; use test output file instead
Merge pull request #2 from dsheets/backtrace

Backtrace
Update alcotest.mli

A typo fixing
Merge pull request #3 from fdagnat/patch-1

Update alcotest.mli