bug#15544: 24.3.50; void variable `universal-argument-num-events'

[Drew Adams]

emacs -Q
M-x set-variable isearch-allow-prefix t
C-s C-3 C-return

Get error:
"Symbol's value as variable is void: universal-argument-num-events"

Grepping for this variable shows that it is not defined anywhere and is
used only in isearch.el (unless it is defined in the C sources).

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-09-30 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --enable-checking 'CFLAGS=-O0 -g3' CPPFLAGS=-DGLYPH_DEBUG=1'