ports/*/jpeg "Thanks a lot guys"

[Buganini]

Recently I'm think about how to make ports easier to upgraded:
1) Add a NODE_VERSION in each ports' Makefile, this variable would be stored
in +CONTENTS.
2) Add a volatile-meaning flag in description of dependencies

When a port, A, whose NODE_VERSION in Makefile > NODE_VERSION in +CONTENTS,
ports that volatile'ly depends on A would be rebuilt.

Any comment is welcome

--Buganini