avoid private stdio fields in waitkey

avoid private stdio fields in waitkey

Use the stdio_ext functions provided by solaris and glibc
instead of directly accessing private stdio FILE structure
members. This is needed for 64-bit solaris builds and is more
portable in general since the FILE structure is meant to be
opaque.  Remove the duplicated code in the pthreaded butc
package.

Change-Id: Idbefa88e2563bb117322e818b1300b324fc3626d
Reviewed-on: http://gerrit.openafs.org/3257
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>