Clean up pred_set/Manual a little.

Prompted by ptroja's commit in cd6153e7.

Note that this material is desperately in need of a more comprehensive
update. The changes here are no more than a hint of how we might more
forward with this (there are similar remnants elsewhere).

In particular, the theorems in pred_set/help/thms should be generated,
and should probably be using EmitTeX technology rather than verbatim
rendering. See also github issue #41. The make process does not
correctly incorporate the manual style .doc entries, and those files
are probably wrong to boot.

pred_set: fixed spaces in PDF manual

duplicate words removed from various documentation files

The magic command is:

grep " \([[:alpha:]]\+\) \1[[:space:]]" \
`find . -name "*.doc" -or -name "*.tex"`

but the output still needs to be filtered by eye, since many duplicates
occur in embedded math and ML.

Duplicates in the Italian manual approved by Domenico Masini.

Remove trailing white-space in a bunch of .tex files.

These are all in src/ and are probably both out-of-date and candidates for removal.

Initial revision