[oe] suggested fixes for docs/usermanual/ directory

[Robert P. J. Day]

  enough little fixes that i'll let someone else decide exactly what
form those fixes will take.

1) Makefile typo:  "sytlesheets" -> "stylesheets"

2) the "clean" target should get rid of generated output files in that
directory, such as ".ps" and ".pdf" files, and any others that might
show up.

3) .gitignore should be extended to include all other possible output
file types, especially "*.ps", which keeps showing up in "git status",
and other possible output directories.

rday
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Robert P. J. Day                               Waterloo, Ontario, CANADA

            Linux Consulting, Training and Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Twitter:                                       http://twitter.com/rpjday
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