intro.1, fork.2, futex.2, open.2, rename.2, select_tut.2, semop.2, spu_create.2,...

intro.1, fork.2, futex.2, open.2, rename.2, select_tut.2, semop.2, spu_create.2, stat.2, netlink.3, random.3, scanf.3, shm_open.3, strftime.3, console.4, console_codes.4, sk98lin.4, st.4, bootparam.7, cpuset.7, credentials.7, man-pages.7, path_resolution.7, uri.7: Global fix: remove spaces around em-dash

Normal English typographical convention is not to have
spaces around em dashes.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>