rebase-interactive: suppress whitespace preceding item count

rebase-interactive: suppress whitespace preceding item count

97f05f43 (Show number of TODO items for interactive rebase, 2014-12-10)
taught rebase-interactive to compute an item count with 'wc -l' and
display it in the instruction list comments:

    # Rebase 46640c6..5568fd5 onto 46640c6 (4 TODO item(s))

On Mac OS X, however, it renders as:

    # Rebase 46640c6..5568fd5 onto 46640c6 (       4 TODO item(s))

since 'wc -l' indents its output with leading spaces. Fix this.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>