[allocator.requirements] Made Tables 27/28 consistent in the use of u.

In other tables of requirements, the identifier 'u' is used for
variables being declared. Made that the case here, too. This
necessitated a reflow of other variable names.
 [sequence.reqmts] Made Table 100 consistent in the use of u.

In other tables of requirements, the identifier 'u' is used for
variables being declared. Made that the case here, too.
[associative.reqmts] Made Table 102 consistent in the use of u.

In other tables of requirements, the identifier 'u' is used for
variables being declared. Made that the case here, too.
[associative.reqmts] Made intro wording for Table 103 more consistent.

Both internally (it was inconsistent in "value" vs. "object") and externally
(Tables 100 and 102 use "value"). While I was at it, fixed capitalization of
the word "table" and fixed up TeX formatting.