RFR: 8270836: Foolproof JavadocTester.checkOutput [v4]

[Pavel Rappo]

> When searching output for multiple strings it is easy to misexpress your intent, which could make a failing test pass. Such cases can be caught and reported to the programmer.
> 
> For example, for this search to succeed it is sufficient for the output to consist only of the `"error: bad"` string:
> 
> 
> checkOutput(..., "error:", "error: bad", ...)

Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:

  Address feedback and more
  
  Search for confusing strings using indexOf. Detect confusing strings across multiple calls to checkOutput. Remove the test which would otherwise have to become very complicated.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4811/files
  - new: https://git.openjdk.java.net/jdk/pull/4811/files/cf1e6a1e..ee5c92f5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4811&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4811&range=02-03

  Stats: 208 lines in 2 files changed: 94 ins; 98 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4811.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4811/head:pull/4811

PR: https://git.openjdk.java.net/jdk/pull/4811