BUG #13002: VACUUM to prevent wraparound blocks TRUNCATE

The following bug has been logged on the website:

Bug reference: 13002
Logged by: Maciek Sakrejda
Email address: maciek(at)heroku(dot)com
PostgreSQL version: 9.3.6
Operating system: Ubuntu 14.04
Description:

If autovacuum is running a VACUUM to prevent wraparound on a certain table,
it looks like it blocks TRUNCATE of that table, which would obviate the need
for the VACUUM in the first place (and could happen much more quickly). This
seems like a usability wart at best--one has to instead kill the autovacuum
(e.g., via pg_cancel_backend) and then TRUNCATE. This is especially
inconvenient when the user trying to truncate does not have permission to
kill (or even see!) the wraparound VACUUM. Would it be possible to have
autovacuum yield to a TRUNCATE in this situation?