make install.do not try changing permissions of existing directories

[nrnrnr]

Except when necessary, I prefer not to install into /usr/local as root. My setup is as follows:

$ ls -ld /usr/local/bin /usr/local/share/man/man1
drwxrwsr-x 3 root staff 4096 Jun  8 11:29 /usr/local/bin
drwxrwsr-x 2 root staff 4096 Oct 12  2021 /usr/local/share/man/man1

Since I'm a member of the staff group it all works out. But running do on install.do failed with an error message:

Installing to: /usr/local
install: cannot change permissions of ‘/usr/local/share/man/man1’: Operation not permitted
install: cannot change permissions of ‘/usr/local/bin’: Operation not permitted

This change calls "$INSTALL" only when the directory to be installed isn't already there.