Merge branch 'fix-includes' into 'master'

fix includes of wait.h and sys/fcntl.h to use standard locations

POSIX standard specifies that wait.h should be in sys/wait.h and
fcntl.h at top-level, not under sys. This is true for all unix systems,
even glibc. glibc provides wait.h and sys/fcntl.h, but these just
includes the same-named headers from the correct locations.

See merge request !26