Construct a completion table like TABLE but with an extra TERMINATOR.
This is meant to be called in a curried way by first passing TERMINATOR
and TABLE only (via `apply-partially').
TABLE is a completion table, and TERMINATOR is a string appended to TABLE's
completion if it is complete. TERMINATOR is also used to determine the
completion suffix's boundary.
TERMINATOR can also be a cons cell (TERMINATOR . TERMINATOR-REGEXP)
in which case TERMINATOR-REGEXP is a regular expression whose submatch
number 1 should match TERMINATOR. This is used when there is a need to
distinguish occurrences of the TERMINATOR strings which are really terminators
from others (e.g. escaped). In this form, the car of TERMINATOR can also be,
instead of a string, a function that takes the completion and returns the
"terminated" string. (fn TERMINATOR TABLE STRING PRED ACTION)