need to implement link(), used by WinSCP

[trel]

When putting a file or overwriting a file via WinSCP...

From NFSRODS log:

2019-09-16 15:18:58.917 ERROR [NFSServerV41] - Unhandled exception:
java.lang.UnsupportedOperationException: Not supported
	at org.irods.nfsrods.vfs.IRODSVirtualFileSystem.link(IRODSVirtualFileSystem.java:789)
	at org.dcache.nfs.vfs.PseudoFs.link(PseudoFs.java:202)
	at org.dcache.nfs.v4.OperationLINK.process(OperationLINK.java:68)
	at org.dcache.nfs.v4.NFSServerV41.NFSPROC4_COMPOUND_4(NFSServerV41.java:204)

Might be possible via GenQuery to ask how many logical paths are pointing to the same physical path on the same resource... If > 1, then do something smart...

[trel]

To provide bidirectionality between hardlinked data objects... this is being addressed as a possible rule engine plugin that provides a set of PEPs to update metadata annotations on data objects marked as hardlinks of one another.

We plan to have an RFC soon and will discuss the approach at the next TWG meeting.

[trel]

This was captured in this RFC:
https://github.com/irods/irods_rfcs/blob/master/0005_hard_links.md

And the first implementation is now here:
https://github.com/irods/irods_rule_engine_plugin_hard_links

[trel]

Awaiting an update to Jargon so NFSRODS can target the specific rule engine plugin on the iRODS server.