(bug 35802) Stop applying unwarranted ellipses to email subjects

When formatting change emails, change subjects being 61, 62 characters
long, were chopped off to 60 characters and had an ellipsis appended.
Hence, the final 63 character long and mangled change subject was
longer than the original change subject. We now make the effective
change subject length limit of 63 more visible and apply an ellipsis
only if needed.

This patch is an adaption of upstream fix from
https://gerrit-review.googlesource.com/#/c/42424/

Change-Id: I41baa8ea843a672e9076dccff0fa7a7af9d4dba7
Merge "(bug 35802) Stop applying unwarranted ellipses to email subjects" into production