[oe] [school] Class 2, Package Versioning Policy

[Holger Freyther]

Hey,

after Koen's introduction to number theory (natural numbers and their order) 
let me continue with a class on Package Versioning.

Let me start with examples

# git-grep "^PV" packages/ | grep "git\\$" | grep SRCREV
packages/mesa/mesa-dri_git.bb:PV = "7.2+git${SRCREV}"
packages/u-boot/u-boot-omap3_git.bb:PV = "2008.10-rc1+${PR}+git${SRCREV}"
packages/xorg-driver/xf86-video-omapfb_git.bb:PV = "0.0.1+${PR}+git${SRCREV}"

Let me go through the errors:
	- As of policy and common standards we want to put a "r" in the revision. 
This means "7.2+gitr${SRCREV}". The same applies to svn, hg, monotone and any 
other scm system supporting a revision. If you checkout by date (SRCDATE) 
remove the "r" or switch the recipe to use SRCREV (this does not work for 
cvs).

       - Okay, never ever put PR into the PV. This is an evil hack and we have 
a known fix and it will land in the OpenEmbedded metadata. SRCPV will land in 
the OE metadata and will solve these issues rendering this hack obsolete.

thanks for listening, a bunch of fixes will come from OM.

	your janitor