- replacement for pretty; app to format a single .go file

printer.go (pkg/go/printer):
- replacement for astprinter.go; implements AST printing
- also replaces pkg/go/ast/format.go for now

cleanups:
- removed/saved away old code

R=r,rsc,iant
DELTA=2833  (1183 added, 1628 deleted, 22 changed)
OCL=30226
CL=30306