Update libtirpc.so library version information

Update libtirpc.so library version information

Bump the library version information for libtirpc to match the latest
version distributed by Red Hat (libtirpc.so.1.0.10).  Without this
change, the latest git repo installs libtirpc.so.1.0.9.

Add an annoying block comment in the Makefile describing how to keep
the library version up to date, 'cause it's kind of confusing, and
apparently entirely unrelated to the package and release version.

Before each release of upstream libtirpc, these version information
rules should be revisited.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>