Comment 2 for bug 1057491

StacktraceTop:
 AptIntf::cancel (this=0x401a920) at apt-intf.cpp:136
 pk_transaction_cancel (transaction=transaction@entry=0x20f8100, context=context@entry=0x7fef04751460, params=<error reading variable: Unhandled dwarf expression opcode 0xfa>) at pk-transaction.c:3274
 pk_transaction_method_call (connection_=<optimized out>, sender=0x7fef10002e10 ":1.106", object_path=<optimized out>, interface_name=<optimized out>, method_name=0x7fef10006250 "Cancel", parameters=0x7fef10006610, invocation=0x7fef04751460, user_data=0x20f8100) at pk-transaction.c:5958
 g_bus_get (bus_type=<optimized out>, cancellable=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at /build/buildd/glib2.0-2.34.0/./gio/gdbusconnection.c:6956
 g_bus_get (bus_type=74781792, cancellable=0x7fef04751460, callback=<optimized out>, user_data=<optimized out>) at /build/buildd/glib2.0-2.34.0/./gio/gdbusconnection.c:6937