less: fix bugs discovered with "git log -p | less -m" on kernel tree

function                                             old     new   delta
read_lines                                           685     733     +48

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
libbb: provide usleep() fallback implementation

POSIX.1-2008 removed the usleep function, provide a fallback
implementaion using the recommended nanosleep().

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>