Tell user when Path Randomization is in effect

[ctrueden]

On recent versions of macOS, if you download an ImageJ distribution such as Fiji and then run it in place, the OS invokes a security feature known as Gatekeeper Path Randomization (GPR). The app gets translocated to a random, temporary, read-only folder e.g.:

ImageJ home: /private/var/folders/n2/5q09bjq11kv6xwpp0xlg4npc0000gq/T/AppTranslocation/FE72DDB9-F7F8-487D-B279-3D7B851F8FCC/d/Fiji.app/
Java home: /private/var/folders/n2/5q09bjq11kv6xwpp0xlg4npc0000gq/T/AppTranslocation/FE72DDB9-F7F8-487D-B279-3D7B851F8FCC/d/Fiji.app/java/macosx/jdk1.8.0_172.jre/jre/Contents/Home

And the ImageJ Updater then fails to be able to update the application, since the installation is read-only and temporary.

I think it is outside the scope of ImageJ to work around this issue. The problem is avoided by copying the application bundle somewhere else such as /Applications. However, the Updater could be smarter about detecting this situation, and giving a friendlier error message telling the user what is going on, and how to fix it.

[ctrueden]

Fixed by 5bd65c8