* Correct buffer_bytes > INT_MAX on BSD/amd64.
The sysctl vfs.bufspace returns either an int or a long, depending on
the value. Large values of vfs.bufspace will result in error messages
like:
couldn't get meminfo: cannot allocate memory
This will detect the returned data type, and cast appropriately.
* Added explicit length checks per feedback.
* Flatten Value() to make it easier to read.
* Simplify per feedback.
* Fix style.
* Doc updates.
