Update to pkg 1.5.99.13 aka 1.6.0 rc3
Changes:

• Important fixes in the solver (fixes the jpeg->jpeg-turbo issue)
• +DISPLAY can now be a ucl file (contextual messages)
• pkg info -D now understand ucl format
• keywords can now define messages to be printed (depending on the context)
• PKG_ROOTDIR is now always set in scripts (default to /)
• pkg version now accept -n <pkgname> to check a given package version against remote repository or ports tree or INDEX file
• Improve Linux support: testuite now passes entirely on linux
• pkg register only tries to load +DESC if it exists