When fixing NMS-5426, Benjamin introduced a change in HttpCollector to let it parse the data according to various locale: first the HTTP response's locale, then openNMS' system locale, then Locale.ENGLISH.

The way HttpCollector tried to devise the HTTP response's locale was flawed.

This patch solves this flaw; Now, HttpCollector devises HTTP responses' locale based on the "Content-Language" HTTP header if present.
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