Add note about libjpeg for PIL (rebased onto dev_4_4)



This is the same as gh-204 but rebased onto dev_4_4.

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If `libjpeg` is not installed while building PIL the JPEG support for some of the python scripts is missing (e.g. the "Split View" from the Figure scripts will fail).

The windows documentation probably doesn't need to be updated since PIL is provided as a binary distribution for that platform (and hopefully comes with JPEG support).