PKG_FLAVOR renamed to PKG_FORMAT in pkgsrc

["Jeremy C. Reed" <reed%reedmedia.net@localhost>]

I committed the rename changes of mk/flavor to mk/pkgformat in pkgsrc. 
This renamed several internal targets.

This is from Anton's work on the Google Summer of Code 2011.

This should currently have zero change on pkgsrc -- there is only one 
PKG_FORMAT and it is "pkg" as it was before.

Hopefully within the next two weeks I will add the mk/pkgformat/rpm 
format and maybe the mk/pkgformat/deb (maybe rename to dpkg?) format.

I have used the PKG_FORMAT=rpm to use "rpm" to create, install, and 
deinstall "rpm" packages using pkgsrc to build them.

  Jeremy C. Reed