Remove spurious spaces.
Add hhvm-nightly builds to the Travis CI build matrix.

Just like the standard hhvm builds, hhvm-nightly is allowed to fail.
Enable fast finishing builds.

The build will be marked as finished as soon as one of the jobs failed
or only jobs allowed to fail are left.

See http://docs.travis-ci.com/user/build-configuration/#Fast-finishing
for details about this feature.
Update ext-libevent version installed for build runs on Travis CI.
Merge branch 'travisci-patches'