userdiff: tighten word-diff test case of the scheme driver

userdiff: tighten word-diff test case of the scheme driver

The scheme driver separates identifiers only at parentheses of all
sorts and whitespace, except that vertical bars act as brackets that
enclose an identifier.

The test case attempts to demonstrate the vertical bars with a change
from 'some-text' to '|a greeting|'. However, this misses the goal
because the same word coloring would be applied if '|a greeting|'
were parsed as two words.

Have an identifier between vertical bars with a space in both the pre-
and the post-image and change only one side of the space to show that
the single word exists between the vertical bars.

Also add cases that change parentheses of all kinds in a sequence of
parentheses to show that they are their own word each.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Scott L. Burson <Scott@sympoiesis.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>