Activate backtrace recording by default

Closes #225
Merge branch 'master' of github.com:mirage/mirage
Fixes in the `V1.STACKV4` to expose UDPv4/TCPv4 types properly

Closes #226
[lib] tweak block and vif lines in sample `.xl` to be more correct
Merge pull request #227 from avsm/master

allow udpv4 packet transmission
Release 1.1.1
Merge branch 'master' of https://github.com/mirage/mirage
Merge branch 'master' into block-nodenumber-hack
[lib] checkpoint