`ant documentation-lint` fails on a checkout with spaces in it [LUCENE-6598]

I haven't yet been able to figure out the cause here, but looks like documentation-lint (and hence precommit) fails on a checkout with spaces in it..

Lots of errors due to checkJavadocLinks.py

```Java
...
[exec] file:///home/ramkrithi/projects/lucene-solr/tr%20unk/solr/build/docs/solr-core/org/apache/solr/search/facet/SumAgg.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
[exec] BROKEN LINK: file:///home/ramkrithi/projects/lucene-solr/tr%2520unk/lucene/build/docs/queries/org/apache/lucene/queries/function/ValueSource.html
...
```

The complaint is actually valid, notice the double escape in the URLs. This seems to affect Solr documentation-lint (Lucene passes) because this problem seems to occur only with the links Javadoc considers "external" (links from Solr to Lucene) and hence puts the full path. Lucene links all have relative paths which don't have this issue.

---
Migrated from [LUCENE-6598](https://issues.apache.org/jira/browse/LUCENE-6598) by Ramkumar Aiyengar (@andyetitmoves)

Start with the ant documentation-lint entry point and checkJavadocLinks.py, reproducing the failure from a checkout whose path contains spaces. Compare the Solr external links with Lucene's relative links and verify that documentation-lint completes without double-escaped paths.

Written by the indexing model from the issue text.