Backport (#517) Add partest interface compile to travis

(cherry picked from commit 2cefff072ae8de907eb4ad9a4cb88e017bf5c3da)

Conflicts:

	.travis.yml
Backport (#517) Fix #538: Correct type signature for append methods on StringBuffer

(cherry picked from commit c16793874c88ac3e185c612715ecfb3585d66639)

Conflicts:

	test/src/test/scala/scala/scalajs/test/javalib/StringBufferTest.scala
Backport (#517) Fix #539: Add files to display tests in Jasmine-HTML

(cherry picked from commit 54e4e57e63152b86c5c98c313bb0a0f3db9087aa)
Remove lingering html files for M7, M8

(from a53fa1bb8bc679eee1ece841c10f87e9edc98417)
Merge pull request #544 from gzm0/backports

Backports to v0.4.x (#517) until aea393caeb01de981aa2fd27f4c1f0eee7003cd7