pkgsrc. Instead, a new variable PKGREVISION is invented that can get
bumped independent of DISTNAME and PKGNAME.
Example #1:
DISTNAME= foo-X.Y
PKGREVISION= Z
=> PKGNAME= foo-X.YnbZ
Example #2:
DISTNAME= barthing-X.Y
PKGNAME= bar-X.Y
PKGREVISION= Z
=> PKGNAME= bar=X.YnbZ (!)
On subsequent changes, only PKGREVISION needs to be bumped, no more risk
of getting DISTNAME changed accidentally.
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