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.
Add a new USE_LIBTOOL definition that uses the libtool package instead of
pkglibtool which is now considered outdated.
USE_PKGLIBTOOL is available for backwards compatibility with old packages
but is deprecated for new packages.
