Compiler handles some URIs incorrectly on Windows (shows in SettingsTests.jarOutput)

[melekhove]

Steps to reproduce from command line:

sbt:dotty> dotc -d out\jaredFoo.jar tests\pos\Foo.scala
[warn] Multiple main classes detected.  Run 'show discoveredMainClasses' to see the list
[info] Running (fork) dotty.tools.dotc.Main -classpath C:\Users\mev\.sbt\boot\scala-2.12.6\lib\scala-library.jar;D:\home
\projects\Scala\Dotty\git\library\..\out\bootstrap\dotty-library-bootstrapped\scala-0.10\dotty-library_0.10-0.10.0-bin-S
NAPSHOT.jar -d out\jaredFoo.jar tests\pos\Foo.scala
Exception in thread "main" java.lang.IllegalArgumentException: Illegal character in opaque part at index 11: jar:file:D:
\home\projects\Scala\Dotty\git\out\jaredFoo.jar
        at java.net.URI.create(URI.java:852)
        at dotty.tools.io.JarArchive$.open(JarArchive.scala:30)
        at dotty.tools.io.JarArchive$.create(JarArchive.scala:20)
        at dotty.tools.dotc.config.Settings$Setting.doSet$1(Settings.scala:150)
        at dotty.tools.dotc.config.Settings$Setting.tryToSet(Settings.scala:180)
        at dotty.tools.dotc.config.Settings$SettingGroup.loop$1(Settings.scala:242)
        at dotty.tools.dotc.config.Settings$SettingGroup.processArguments(Settings.scala:248)
        at dotty.tools.dotc.config.Settings$SettingGroup.loop$1(Settings.scala:243)
        at dotty.tools.dotc.config.Settings$SettingGroup.processArguments(Settings.scala:248)
        at dotty.tools.dotc.config.Settings$SettingGroup.processArguments(Settings.scala:256)
        at dotty.tools.dotc.config.CompilerCommand$.distill(CompilerCommand.scala:61)
        at dotty.tools.dotc.Driver.setup(Driver.scala:47)
        at dotty.tools.dotc.Driver.process(Driver.scala:133)
        at dotty.tools.dotc.Driver.process(Driver.scala:103)
        at dotty.tools.dotc.Driver.process(Driver.scala:115)
        at dotty.tools.dotc.Driver.main(Driver.scala:142)
        at dotty.tools.dotc.Main.main(Main.scala)
Caused by: java.net.URISyntaxException: Illegal character in opaque part at index 11: jar:file:D:\home\projects\Scala\Do
tty\git\out\jaredFoo.jar
        at java.net.URI$Parser.fail(URI.java:2848)
        at java.net.URI$Parser.checkChars(URI.java:3021)
        at java.net.URI$Parser.parse(URI.java:3058)
        at java.net.URI.<init>(URI.java:588)
        at java.net.URI.create(URI.java:850)
        ... 16 more
[error] Nonzero exit code returned from runner: 1
[error] (dotty-compiler / Compile / runMain) Nonzero exit code returned from runner: 1
[error] Total time: 4 s, completed 25.09.2018 7:00:41