RFR : 8207395: jar has issues with UNC-path arguments for the jar -C parameter [windows]

[Baesken, Matthias]

Please review   this small fix for allowing  windows UNC paths  in the  jar -C  parameter.
Currently  passing a UNC path to a directory   with -C <dir>   fails  :

c:\testdir>c:\tools\jdk10\bin\jar.exe test.jar -C \\MYMACHINE\subdir README.txt
Illegal option: s
Try `jar --help' for more information.

With  the patch  it works .

webrev

http://cr.openjdk.java.net/~mbaesken/webrevs/8207395/

bug

https://bugs.openjdk.java.net/browse/JDK-8207395




Thanks, Matthias