This question actually has two parts: (1) Should an abbreviation such as Jr for Junior include a period at all? (2) If the abbreviation does take a period and if it appears at the end of a sentence, should the sentence be punctuated to include both the Jr period and the end-of-sentence period? The answers to both questions are matters of house style, and consequently may vary from publisher to publisher and from style manual to style manual.
Having said that, I don't think that I've ever seen a house style guide in the United States that endorsed the use of consecutive periods in this situation. Most U.S. publishers intentionally or coincidentally follow the Chicago Manual of Style, Fifteenth Edition (2003) on this point:
6.122 No double period. When an expression that takes a period ends a sentence, no additional period follows [cross reference omitted]. ... [Example:] The study was funded by Mulvehill & Co.
As for Wikipedia's house rule, you can find a relevant discussion (dated 26 April 2009) in Wikipedia's Help Desk Archives, under the heading Jr. at end of sentence. The upshot of the discussion appears to be that ending a sentence with "Jr.." is not consistent with Wikipedia style.