Enable email notifications from Travis CI

http://docs.travis-ci.com/user/notifications/
> By default, email notifications will be sent to the committer and the commit author, if they are members of the repository (that is, they have push or admin permissions for public repositories, or if they have pull, push or admin permissions for private repositories).
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> And it will by default send emails when, on the given branch:
>
> * a build was just broken or still is broken
> * a previously broken build was just fixed
Include some jemalloc stats in the -m measurements.
Add stringcache to build, now that phf is working on android
Remove the unused window field from ValidityState.

It is only necessary if the ValidityState would create new objects, which it
doesn't.
Remove the unused 'obj' local from the construct hook.
Simplify the initialization of Performance.
Remove the unused window field from NodeList.
Remove the unused window field from HTMLCollection.
Remove the unused window member of AttrList.
Remove the unused window field from File.
Merge pull request #2827 from glennw/add-string-cache

Add stringcache to build, now that phf is working on android
Merge pull request #2800 from SimonSapin/travis-email

Enable email notifications from Travis CI
Merge pull request #2832 from Ms2ger/nodelist-window

Remove the unused window fields from NodeList and HTMLCollection; r=Manishearth
Merge pull request #2831 from Ms2ger/perf-cleanup

Simplify the initialization of Performance; r=Manishearth
Merge pull request #2829 from Ms2ger/validitystate-window

Remove the unused window field from ValidityState; r=Manishearth
Merge pull request #2803 from nnethercote/jemalloc-stats

Include some jemalloc stats in the -m measurements.
Return slices from get_attribute_parts.
Merge pull request #2834 from Ms2ger/file-window

Remove the unused window field from File; r=Manishearth
Merge pull request #2833 from Ms2ger/attrlist-window

Remove the unused window member of AttrList.
Fix comments in image_cache_task

The Cell that used to be here is now gone, and there is a typo in
another comment.