emacs: Fix search tab completion in terminals
In X, Emacs distinguishes the tab key, which produces a 'tab event;
from C-i, which produces a ?\t event. However, in a terminal, these
are indistinguishable and only produce a ?\t event. In order to
simplify things, Emacs automatically translates from 'tab to ?\t (see
"Function key translations" in M-x describe-bindings), so functions
only need to be bound to ?\t to work in all situations.
Previously, the search tab completion code usedq (kbd "<tab>"), which
produced the event sequence [tab], which only matched the 'tab event
and hence only worked in X. This patch changes it to (kbd "TAB"),
which matches the general ?\t event and works in all situations.