build: install programs as owner rw (#3)

build: install programs as owner rw (#3)

Principle of least privilege suggests that for security-relevant
programs, no permissions other than those strictly necessary should be
applied. Hence the historic permissions for fcron were "executable, and
that's it". However, this causes problems for some legitimate use cases,
such as analysis of soname dependencies via readelf, use of strip, etc.

Slightly relax the install permissions to grant the owner, at least, rw
permissions. The owner can already trivially obtain these permissions at
will using chown, this merely saves them the bother.

Fixes #2