Adjustment to Portage soname resolution logic

It may be necessary to adjust Portage soname resolution logic in order to account for special circumstances. For example, Portage soname resolution tolerates missing DT_SONAME for dynamic libraries that a package installs in a directory that its binaries reference via DT_RUNPATH. This behavior is useful for packages that have internal dynamic libraries stored in a private directory. An example is ebtables, as discussed in bug 646190.