Fix end of sentence spacing in man pages, and related problems.

Fix end of sentence spacing in man pages, and related problems.
troff(1) input that ends a sentence at the end of the line gets the
proper inter-sentence spacing when formatted.  If the sentence ends
midline then two spaces must follow to get the same result, otherwise
the spacing looks odd.  Similarly, if a full stop is not the end of a
sentence then it should have the zero-width escape appended so if
re-formatting the source happens to place it at the end of the line then
no large gap follows it: e.g. `e.g.\&'.
Replace `et. al.' with `et al'.