improve jtidy javadocs check [LUCENE-4505]

[asfimport]

Currently we are using the ant task (http://sourceforge.net/p/jtidy/code/1261/tree/trunk/jtidy/src/main/java/org/w3c/tidy/ant/JTidyTask.java) built into jtidy itself.

This has a number of disadvantages:

• at least in the version we are using, creates a ByteArrayDataOutput that hides all the output. So if there is an error, its no good.
• requires creation of a temp directory: even though we disable the actual output with a parameter, this means it creates thousands of 0 byte files

We only pass 3 options to tidy today:

• input-encoding=UTF-8
• only-errors=true
• show-warnings=false <-- this one is a OOM hack.

Ideally i think we would:

• pass input-encoding=UTF-8, only-errors=true, quiet=true.
• send all output to a single file or property.
• if this contains any contents, fail and print the contents.

This would mean we would fail on warnings too (I checked, this is a good thing, there would be some things to fix).
So as a start we could just set show-warnings=false temporarily so we only fail on errors like today.

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Migrated from LUCENE-4505 by Robert Muir (@rmuir)

[asfimport]

Robert Muir (@rmuir) (migrated from JIRA)

Here is the commandline equivalent: say i screw up our lucene/docs/index.html and add a unclosed bold tag in the getting started paragraph,
and a bogus tag at the end:

rmuir@beast:\~/workspace/lucene-trunk/lucene/build/docs$ java -jar \~/Downloads/jtidy-r938.jar -e -q index.html
line 1 column 1 - Warning: missing <!DOCTYPE> declaration
line 24 column 62 - Warning: missing </b> before </p>
line 27 column 1 - Warning: inserting implicit <b>
line 111 column 1 - Error: <dfdsfdsf> is not recognized!
line 111 column 1 - Warning: content occurs after end of body
line 111 column 1 - Warning: discarding unexpected <dfdsfdsf>
line 112 column -3 - Warning: content occurs after end of body
line 112 column -3 - Warning: discarding unexpected </dfdsfdsf>

Basically we want to fail if there is any output like this at all. Note only one of the problems is an error!
The "Warnings" are also bogus things we should fix.

NOTE: there are some "false" warnings that are bugs in 'javadocs itself', but it seems we could just filter those out:

rmuir@beast:\~/workspace/lucene-trunk/lucene/build/docs$ java -jar \~/Downloads/jtidy-r938.jar -e -q core/deprecated-list.html 
line 152 column 20 - Warning: <a> escaping malformed URI reference

Thats because javadoc generates bogus urls like <a href="org/apache/lucene/search/FuzzyQuery.html#floatToEdits(float, int)">
instead of escaping with %20...