https://reviews.freebsd.org/D20651 had some mistakes, fix these with an updated patch.
The current postfix conversions are:
- CURRENT / STABLE -> .sYYYYMMDDhhmmss
- ALPHAx -> .ax, so 11.3-ALPHA1 becomes 11.3.a1
- BETAx -> .bx, so 12.1-BETA2 becomes 12.1.b2
- RCx -> .rx, so 13.0-RC3 becomes 13.0.r3
- PRERELEASE -> .p, so 11.3-PRERELEASE becomes 11.3.p
- RELEASE -> (nothing), so 12.1-RELEASE becomes 12.1
For any -pX, a package revision of X is added, so 12.1-BETA2-p3 becomes 12.1.b2_3