namespace conformance to latest standards in strings.h
implement non-stub strverscmp

patch by Isaac Dunham.
fix integer type issue in strverscmp

lenl-lenr is not a valid expression for a signed int return value from
strverscmp, since after implicit conversion from size_t to int this
difference could have the wrong sign or might even be zero. using the
difference for char values works since they're bounded well within the
range of differences representable by int, but it does not work for
size_t values.
fix cruft in utmp.h that was broken by changes in utmpx.h

patch by Chris Spiegel.
Merge branch 'master' of git://git.musl-libc.org/musl into fixes