New version of the FX-aware jcheck

[Kevin Rushforth]

For those using the modified jcheck as indicated on the OpenJFX Wiki [1] 
be aware that the latest promoted build tags, which were just synced 
into the jfx-dev/rt repo, will require you to download a new version of 
the modified jcheck tool [2] to handle the new tag format.

-- Kevin

[1] https://wiki.openjdk.java.net/display/OpenJFX/Using+jcheck
[2] http://cr.openjdk.java.net/~kcr/jcheck/bin/jcheck.py