Backport (#517) Fix #499: Emit opaque URI in positions for virtual Scala files

(cherry picked from commit fe5a9c69d959817c82b66f19e2e2ee852b03b9fa)

Conflicts:
	compiler/src/main/scala/scala/scalajs/compiler/GenJSCode.scala
	compiler/src/test/scala/scala/scalajs/compiler/test/util/JSASTTest.scala
Backport (#517) Fix #525: Closure emits spurious warnings for @JSExported properties.

(cherry picked from commit 8d2111457cff2bfc05ff91f731cd5c208a70d729)
Backport (#517) Fix #518: Closure sometimes eliminates all our exports.

(cherry picked from commit 8793d47c9f88def176e927a2296fb82db893859a)
Backport (#517) Report call stack when warning for non-existent class.

(cherry picked from commit 702d8d2b95208c4400e7da7a76792bd37880e30d)

Conflicts:
	tools/src/main/scala/scala/scalajs/tools/optimizer/Analyzer.scala
Merge pull request #531 from gzm0/backports

Backports to v0.4.x (#517) until c83355646e3b6d99fec3beb3bb85debde5cd098a
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
Version 0.4.4.