[development] new install hook examples, .install files

i spent a few hours getting my HEAD modules using the new core install hook. i found the developer docs to be just a bit confusing, but was able to get things right after a bit. anybody who's interested in looking at some working examples, see eventrepeat.install or signup.install in HEAD contrib. since the hook is called from a full bootstrap, you can actually do a heck of a lot more than just install tables--in my case i also displayed some user messages regarding the status of the module installation, and in eventrepeat's case, i invoked eventrepeat_cron() to autopopulate a table w/ current date information. i'm loving this change! :) chad