dabbrev-expand syntax not working good in many modes

[Dan Jacobson]

You know, I find that for plenty of various computer language modes,
dabbrev-expand has not been sensitized to word boundaries correctly.
For instance here "|" is not seen to break words here in bash mode:
C-x C-f / t m p / a . s h <return> a a a a | b b b b | a <escape> /

[one wants an "aaaa" to appear.]  Anyways, for many of these
situations one must put unnecessary whitespace surrounding various
reserved tokens to get dabbrev-expand to work nicely.
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