Hello,

This modifies the memory read/write functions so that they strongly 
prefer the inferior's to_xfer_partial method over the older 
to_xfer_memory method.

With this in place the need to implement xfer_memory is eliminated - I 
deleted the function from inf-ptrace.c - inferiors (namely GNU/Linux) 
can more easily overide the inherited xfer method.

committed,
Andrew

(and I thought getting GNU/Linux using inferior inheritance was be easy)