Enforcing the version of the compiler might be good to catch errors on the release manager side, however it makes a PITA for anyone that wants to build the release for internal purposes. There are good reasons (we actually recommend it in the README IIRC) to rebuild with 1.3 if you are stuck in a legacy environment.
I'd suggest to back that patch out from build.xml and add an internal, non-commented (so that it does not show up in "ant -p") target, e.g. dist-package, that is used by the release manager to build the distribution.
I also would like to see this clearly documented in the velocity docs.
That is the kind of "last minute rush" patches, that I did want to avoid. That patch should IMHO not have been in the 1.5 release, that would have been good for 1.5.1 or 1.6