spec: Update polkit dependencies for CVE-2013-4311

Use secured polkit on distros which provide it. However, RHEL-6 will
still allow for older polkit-0.93 rather than forcing polkit-0.96-5
which is not available in all RHEL-6 releases.

libvirt.spec.in

@@ -535,7 +535,9 @@ BuildRequires: module-init-tools
 BuildRequires: cyrus-sasl-devel
 %endif
 %if %{with_polkit}
-    %if 0%{?fedora} >= 12 || 0%{?rhel} >= 6
+    %if 0%{?fedora} >= 20 || 0%{?rhel} >= 7
+BuildRequires: polkit-devel >= 0.112
+    %elif 0%{?fedora} >= 12 || 0%{?rhel} >= 6
 BuildRequires: polkit-devel >= 0.93
     %else
 BuildRequires: PolicyKit-devel >= 0.6
@@ -698,7 +700,9 @@ Requires: avahi-libs
         %endif
     %endif
     %if %{with_polkit}
-        %if 0%{?fedora} >= 12 || 0%{?rhel} >=6
+        %if 0%{?fedora} >= 20 || 0%{?rhel} >= 7
+Requires: polkit >= 0.112
+        %elif 0%{?fedora} >= 12 || 0%{?rhel} >=6
 Requires: polkit >= 0.93
         %else
 Requires: PolicyKit >= 0.6