Logical 'or' for package dependencies

[rarob at travelinglightfarm.net]

Quick question (I hope).  Suppose you are making a package that requires
Java.  Either OpenJDK -or- SUN/Oracle is acceptable.  OpenJDK provides the
'openjdk' package, whereas SUN/Oracle provides 'jre' for the basic
runtime.  How would one craft the 'Requires:' line to pass if either (or
both) is present?

Or do we to provide 2 RPMs, one for each flavor of Java...

-Rob