Fix #58 (SI-4528) BasicTransformer has no longer exponential complexity

[biswanaths]

Replaced the transform(ns) // tranform sequence with one of the proposed methodhttps://issues.scala-lang.org/browse/SI-4528

Added tests to verify that the transform is reusing all the nodes it should be, also equivalency of the original, modified and the alternate option.

Please let me know, if there are any issue with the pull request.

[adriaanm]

LGTM -- would be good to fix typos in commit message, include the longer description from the PR, and mention the github issue as "Fixes #58", which will cause github to cross-link.

I suggest a title like "Fix #58 (SI-4528) BasicTransformer no longer exponential"

[adriaanm]

Thanks, @biswanaths! I'll add you to the scala-xml admins so you can merge go through the other PRs and merge those that are ready.

[biswanaths]

@adriaanm , updated the commit message to follow the standards as suggested by you.

[adriaanm]

Thanks! I'll let you do the honors :)