[yocto] Debugging opkg installs

[Matt Schuckmann]

I'm looking for some tips on debugging package install problems. 
Recently I've had a problem where edits to a pkg_postinst function in one of my recipes was not getting run when rebuilding my image. The only way I could get the pkg_postinst() function to run was to wipe out my complete openembedded build/tmp directory and let it rebuild everything from scratch (and the sstate cache). I'd really like to understand what was going on here. My guess is there was some sort of flag somewhere that was telling the opkg to not run the postinst script for that package because it had already been done once. 

It would also be nice to know how to run opkg installs locally on my dev system to test out recipes but I haven't quite worked out the right tools in place on my dev system and or what the right commands are.

Thanks,
Matt S.