Fix some overfull hbox problems in the ebook version

There are some severe overfull hbox problems  (i.e. _truncated_ lines!) in the ebook version (and presumably also the ustrade version): see, for instance, pp 77, 120, and 202 in the original released version, or pp 79, 122, and 204 in the version of commit 7de3423000c2069ad51c07657376532fc2af4708.

Long mathematical expressions like that on p. 79 can be broken up by inserting `\allowbreak` at appropriate points, and problems like on p. 204 can be fixed by inserting discretionary hyphens (or `\allowhyphens` from the ), but I'm afraid more substantial changes are needed to fix problems like that on p. 122. (In the attached patch, I just insert a ragged line break, which looks bad but does the job.)