RFR: 8280903: javadoc build fails after JDK-4774868

[Brian Burkhalter]

Prefix `java.io` to FOS and RAF links.

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Commit messages:
 - 8280903: javadoc build fails after JDK-4774868

Changes: https://git.openjdk.java.net/jdk/pull/7273/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7273&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280903
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7273.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7273/head:pull/7273

PR: https://git.openjdk.java.net/jdk/pull/7273