Allow the user to specify precise-exception behaviour for translations
made from file-backed mappings (AOT code, basically) that is different
from the default behaviour as specified by --vex-iropt-register-updates.

New flag is --px-file-backed=, with the same possible args as
--vex-iropt-register-updates has.

Add a new flag --px-default, which is a short alias for

Add one line of stats output when --stats=yes, showing counts of how
many translations have been made under each of the 4 different PX
optimisation settings.

No user-visible change if you don't use the new flags.

Relies on VEX API change in r3084.

git-svn-id: svn:// a5019735-40e9-0310-863c-91ae7b9d1cf9
8 files changed