Add CMake macro find_so_name(). #374

Given the full path to a shared library file, return the SO name of
that library. For example, the SO name of "/usr/lib64/libssl.so" is
"libssl.so.10" in the current release of Red Hat 6.
The result is indicated to be used with dlopen().
Only supported on Linux.
dlopen() libssl and kerberos when needed by CEDAR on linux. #374

This reduces memory usage when these authentication methods aren't used,
which is especially noticeable in the shadow. If dlopen()/dlsym() fail,
then we ignore that authentication method.

The collector and schedd still need to link against these libraries for
gsoap.
Remove unused external krb5-1.10. #374