non-standard but common types.  Including Martin's suggestion to add
rejected non-standard types from patch #438790.  Specifically,

guess_type(), guess_extension(): Both the functions and the methods
grow an optional "strict" flag, defaulting to true, which determines
whether to recognize non-standard, but commonly found types or not.

Also, I sorted, reformatted, and culled duplicates from the big
types_map dictionary.  Note that there are a few non-equivalent
duplicates (e.g. .cdf and .xls) for which the first will just get
thrown away.  I didn't remove those though.

Finally, use of the module as a script as grown the -l and -e options
to toggle strictness and to do guess_extension(), respectively.

Doc and unittest updates too.