Replace the fallback of avr_read_byte() and avr_write_byte() to

avr_read_byte_default() and avr_write_byte_default (resp.) by directly
calling the latter functions from within all programmers that don't
implement their own read_byte()/write_byte() methods.  In turn, make the
read_byte() and write_byte() methods mandatory, and the cmd() method
(direct ISP command) optional instead (it's effectively mandatory for
any programmer using avr_read_byte_default()/avr_write_byte_default()
though).  Remove all the pointless cmd() method stubs from those programmers
that don't need it.

Eliminate avr_read_byte() as it was now completely identical to
pgm->read_byte().


git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude@684 81a1dc3b-b13d-400b-aceb-764788c761c2

par.c

@@ -425,6 +425,8 @@ void par_initpgm(PROGRAMMER * pgm)
   pgm->getpin         = par_getpin;
   pgm->highpulsepin   = par_highpulsepin;
   pgm->parseexitspecs = par_parseexitspecs;
+  pgm->read_byte      = avr_read_byte_default;
+  pgm->write_byte     = avr_write_byte_default;
 }
 
 #else  /* !HAVE_PARPORT */