Changed install targets so
(1) "make install" installs everything;
(2) more directories are built as needed;
(3) the X11R5 shell script install-sh is used (always).
(The script can't be called install.sh since some Make versions have a
default rule that copies "foo.sh" to "foo" when making "foo".)

Added target "smelly" which checks for non-Py-prefixed exported
symbols.