Fixes output to file when multiple errors on different sources.

[Cayan]

Only the last file with errors is being reported.

Updated version of @gronke's pull request (just the fix, without the tests)

[palantirtech]

Thanks for your interest in palantir/grunt-tslint, @Cayan! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[Cayan]

The result from the generated file is not a proper pmd file. Jenkins PMD Plugin failed to import it.

Generated sample:

<pmd version="tslint"><file ...></file></pmd><pmd version="tslint"><file ...></file></pmd><pmd version="tslint"><file ...></file></pmd>...<pmd version="tslint"><file ...></file></pmd>

[gronke]

#31 is rebased and cleaned (including the tests)

@Cayan thanks for reviving this. Do you have a suggestion how to fix the Jenkins import? Looks like a different issue than this PR attempts to solve..

[Cayan]

@gronke I'm working on it. This is a TSLint bug as well. Fixed here: palantir/tslint#1493

[Cayan]

Jenkins successfully imported the reported PMD file with both PR's content.

[Cayan]

A previous PR was opened with the solution for the XML bug palantir/tslint/pull/1472, so I closed my PR there. Since this implementation needed palantir/tslint#1493, it will now be closed. A proper implementation should be created with the first strategy.