* The build can't descend into external submodules when there is no
configure/RULES_TOP file present in $(INSTALL_LOCATION).
* Recreate modules/RELEASE.<host>.local if configure/CONFIG_SITE or
configure/CONFIG_SITE.local have changed.
* Move the distclean of modules/RELEASE.<host>.local to RULES_TOP
* Several comment and white-space changes
Adds PARENT_MODULE to detect when building a submodule.
RULES_TOP uses that to disable uninstall rules and abort instead of
deleting the parent's configure/ directory.
