virDomainBlockPeek call

* configure.in: Document AC_SYS_LARGEFILE.
	* docs/hvsupport.html.in: Document HV support for virDomainBlockPeek.
	* include/libvirt/libvirt.h.in, src/driver.h, src/libvirt.c,
	src/libvirt_sym.version: Add virDomainBlockPeek infrastructure.
	* src/qemu_driver.c, src/test.c: Null versions of this call.
	* src/xen_unified.c, src/xend_internal.c, src/xend_internal.h,
	src/xm_internal.c, src/xm_internal.h: Xen implementation.
	* tests/sexpr2xmldata/sexpr2xml-curmem.xml,
	tests/sexpr2xmldata/sexpr2xml-no-source-cdrom.xml: XML output
	has been reordered slightly in the Xen driver, but should be
	functionally the same.

tests/sexpr2xmldata/sexpr2xml-curmem.xml

@@ -15,17 +15,17 @@
   <on_reboot>restart</on_reboot>
   <on_crash>restart</on_crash>
   <devices>
+    <disk type='file' device='disk'>
+      <driver name='tap' type='aio'/>
+      <source file='/xen/rhel5.img'/>
+      <target dev='xvda' bus='xen'/>
+    </disk>
     <interface type='bridge'>
       <source bridge='xenbr0'/>
       <target dev='vif5.0'/>
       <mac address='00:16:3e:1d:06:15'/>
       <script path='vif-bridge'/>
     </interface>
-    <disk type='file' device='disk'>
-      <driver name='tap' type='aio'/>
-      <source file='/xen/rhel5.img'/>
-      <target dev='xvda' bus='xen'/>
-    </disk>
     <input type='mouse' bus='xen'/>
     <graphics type='vnc' port='-1'/>
     <console type='pty'>

tests/sexpr2xmldata/sexpr2xml-no-source-cdrom.xml

@@ -20,11 +20,6 @@
   <clock offset='utc'/>
   <devices>
     <emulator>/usr/lib/xen/bin/qemu-dm</emulator>
-    <interface type='bridge'>
-      <source bridge='xenbr0'/>
-      <target dev='vif6.0'/>
-      <mac address='00:16:3e:0a:7b:39'/>
-    </interface>
     <disk type='block' device='disk'>
       <driver name='phy'/>
       <source dev='/dev/sda8'/>
@@ -34,6 +29,11 @@
       <target dev='hdc' bus='ide'/>
       <readonly/>
     </disk>
+    <interface type='bridge'>
+      <source bridge='xenbr0'/>
+      <target dev='vif6.0'/>
+      <mac address='00:16:3e:0a:7b:39'/>
+    </interface>
     <input type='mouse' bus='ps2'/>
     <graphics type='vnc' port='-1'/>
     <serial type='pty'>