Avoid triggering a rerun of all do_package* tasks when OEBasicHash
signature generator is being used and the buildhistory package code or
any of the package related variables change.
Note that adding and removing INHERIT of buildhistory will still force
this rebuild - use the newly added BUILDHISTORY_FEATURES variable to
enable and disable buildhistory instead in order to avoid this.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
