Fix TranslatingPort access functions to:

Fix TranslatingPort access functions to:
- know nothing about Fault objects (as it should be)
- call fatal() by default on accesses to unmapped addrs
- provide "try" versions for callers that are prepared to handle failure

mem/translating_port.cc:
mem/translating_port.hh:
    Memory system objects should not return Fault objects, just errors.
    Half the time we don't check the return code anyway, so make
    default version of the access functions call fatal().
    Provide "try*" versions that return a bool for places where we
    really are going to check the return code.
sim/syscall_emul.cc:
sim/syscall_emul.hh:
    Need to use new "tryReadString" here since we actually check the return code.

--HG--
extra : convert_revision : 039737398ef183904dc382c05912ab96cd1d4a51