René Scharfe authored May 28, 2016 and Junio C Hamano committed May 31, 2016

The function trim_common_tail() exits early if context lines are
requested.  If -U0 and -W are specified together then it can still trim
context lines that might belong to a changed function.  As a result
that function is shown incompletely.

Fix that by calling trim_common_tail() only if no function context or
fixed context is requested.  The parameter ctx is no longer needed now;
remove it.

While at it fix an outdated comment as well.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>