main/xen: security upgrade to 4.2.5 and patches

The 4.2.5 release fixes:
CVE-2014-2599 / XSA-89 HVMOP_set_mem_access is not preemptible
CVE-2014-3124 / XSA-92 HVMOP_set_mem_type allows invalid P2M entries to be
                       created
CVE-2014-3967,CVE-2014-3968 / XSA-96 Vulnerabilities in HVM MSI injection
CVE-2014-4021 / XSA-100 Hypervisor heap contents leaked to guests

In addition we add patches for:
CVE-2014-7154 / XSA-104 Race condition in HVMOP_track_dirty_vram
CVE-2014-7155 / XSA-105 Missing privilege level checks in x86 HLT, LGDT,
                        LIDT, and LMSW emulation
CVE-2014-7156 / XSA-106 Missing privilege level checks in x86 emulation of
                        software interrupts
CVE-2014-7188 / XSA-108 Improper MSR range used for x2APIC emulation

fixes #3412
fixes #3457