RFR: Alex review

[Chris Plummer]

Minor fixes based on input from Alex

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Commit messages:
 - Make trackVthreads final.
 - Fix freeing of memory in getAllThreads() when there is an error.
 - Get rid of unnecessary language for when both filters are added.
 - Clean up wording for OPAQUE_FRAME error with ForceEarlyReturn

Changes: https://git.openjdk.java.net/loom/pull/149/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=149&range=00
  Stats: 20 lines in 6 files changed: 3 ins; 11 del; 6 mod
  Patch: https://git.openjdk.java.net/loom/pull/149.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/149/head:pull/149

PR: https://git.openjdk.java.net/loom/pull/149