pkgbase: differentiate package versions for ALPHA/BETA/PRERELEASE/RC phases
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 -> .rcx, so 13.0-RC3 becomes 13.0.rc3 PRERELEASE -> .p, so 11.3-PRERELEASE becomes 11.3.p RELEASE -> (nothing), so 12.1-RELEASE becomes 12.1
Submitted by: rene (original version)
Differential Revision: https://reviews.freebsd.org/D20734