To date, our implementation of munmap(2) has required that the
entirety of the specified range be mapped. Specifically, it has
returned EINVAL if the entire range is not mapped. There is not,
however, any basis for this in either SuSv2 or our own man page.
Moreover, neither Linux nor Solaris impose this requirement. This
revision removes this requirement.

Submitted by: Tijl Coosemans
PR: 118510
MFC after: 6 weeks