RFR JDK-8147539: (zipfs) ZipPath should throw ProviderMismatchException when invoking register()

[Xueming Shen]

Hi,

Please help review the changes for the following zipfs related bug fixes

JDK-8147539: (zipfs) ZipPath should throw ProviderMismatchException when 
invoking register()
JDK-8153248: (zipfs) ZipPath#getFileName( ) returns inconsistent result
JDK-8146754: (zipfs) ZipPath.relativize() returns wrong result for path 
ending with slash /
JDK-8139956: (zipfs) ZipPath does not produce correct empty path on 
relativize()

issue:
https://bugs.openjdk.java.net/browse/JDK-8147539
https://bugs.openjdk.java.net/browse/JDK-8153248
https://bugs.openjdk.java.net/browse/JDK-8146754
https://bugs.openjdk.java.net/browse/JDK-8139956

webrev:
http://cr.openjdk.java.net/~sherman/8139956_8146754_8147539_8153248/webrev/

The changes are relative easy.
(1) ZipPath.initOffsets() should deal with empty path specially, as the 
UnixPath impl does
(2) ZipPath.normalize(byte[]) should take care of tailing "/" (it is 
taken care of at
       ZipPath.normalize(byte[], int), but is missed in the "main" method)
(3) ZipPath.register() should throw PME as suggested.

Thanks,
Sherman