RFR: 8148626: URI.toURL needs to use protocol Handler to parse file URIs

[Claes Redestad]

Hi,

it turns out trying to optimize URI to URL conversion for file URLs 
don't work out very well due to special treatment of backward slashes.

Instead of trying to deal with such file URLs, this patch partially 
backs out 8147462 and only leave the optimization in place for the jrt 
protocol. This still helps
reducing footprint in jigsaw while keeping things performance neutral 
for other kinds of URLs.

Bug: https://bugs.openjdk.java.net/browse/JDK-8148626
Webrev: http://cr.openjdk.java.net/~redestad/8148626/webrev.01/

/Claes