Make sure locally created files are not owned by root after doing build as sudo.
Make sure locally created files are not owned by root after doing build as sudo.

So, if you're running build under sudo, we change the owner and group of all
locally created files to the underlying non-privileged user $SUDO_USER.  That
way you don't have any files annoyingly owned by root in your local directory.

Here's a clear-cut test case which now works:

	sudo ./build quiet clean install
	./build quiet clean install in ~/myfexl

Before the change, you'd get a bunch of errors on the second command as it
tried to delete object files owned by root created in the first command.  With
the change, everything works smoothly.

Here's another clear-cut test case:

	sudo ./build quiet clean
	./build erase

chkoreff/Fexl,chkoreff/Fexl