* (bug 12130) Initial newlines are now preserved correctly during editing

* (bug 12130) Initial newlines are now preserved correctly during editing

HTML browsers strip the first newline from the literal contents of a <textarea>, but keep any additional newlines beyond that.

Prepending an extra newline in Html::textarea() when the contained text started with a newline makes our output basically look like this:

<textarea>             <-- (this added newline is ignored)
                       <-- (any original newline here is preserved)
blah blah</textarea>

This seems to consistently resolve the stripping of single initial newlines from every edit operation as seen on bug 12130; as noted on comments there <https://bugzilla.wikimedia.org/show_bug.cgi?id=12130#c17> this had deleterious effects on Wikisource, where transcription/proofreading tends to involve breaking up lots of little pages, which may have a significant newline at the start of a page boundary.

Text that didn't have initial newlines won't see any difference in the HTML output.

Followup to test cases in r98576, which confirm that supported browsers consistently have this behavior.