Adding a suppression file reduces the number of false positives from memcheck. Run with:
```
valgrind --suppressions=etc/valgrind-memcheck.supp servo ...
```
For the moment, this just switches off the warnings generated by jemalloc.
Source-Repo: https://github.com/servo/servo
Source-Revision: f3e921a584e4254ff009c0494c48f9e3b6559c91
Alan Jeffrey