Add strlcat and strlcpy to libafsauthent and libafsrpc

Add strlcat and strlcpy to libafsauthent and libafsrpc

Other functions included in libafsauthent and libafsrpc are using strlcpy
and strlcat, so include those objects in the libraries so that they stay
self-contained.

strlcat and strlcpy shouldn't be part of the public API for the libraries,
for various reasons including the fact that they're not built on all
platforms.  Therefore, don't add the functions to the library exports and
include them separately in each library.

Reviewed-on: http://gerrit.openafs.org/63
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Verified-by: Derrick Brashear <shadow@dementia.org>