These example programs are derived from long-running (>15 minutes) tests
in the test suites of highly-downloaded crates. They should serve as
realistic but also somewhat pathological workloads for the interpreter.
The unicode program stresses the code which looks for adjacent and equal
stacks to merge them.
The backtrace program has an uncommonly large working set of borrow tags
per borrow stack.
This also updates the .gitignore to ignore files commonly emitted in the
course of using these benchmark programs.
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