library: Add an accessor for the real SONAME

Includes !128 (merged), please review that first.

/cc @denittis

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• library: Distinguish between requested name and SONAME

  In rare cases, like libldap-2.4 and libcurl in scout, they can differ.

• library: Add an accessor for the real SONAME

  In s-r-system-info, we show libraries whose SONAME is not the same as the name we asked for, even in non-verbose mode. For example, if the expectations have not been updated to list libldap_r-2.4.so.2 yet, Debian systems will show:

    "libldap-2.4.so.2" : {
      "soname" : "libldap_r-2.4.so.2",
      "path" : "/usr/lib/x86_64-linux-gnu/libldap-2.4.so.2"
    },