os: New Open API.

We replace the current Open with:
OpenFile(name, flag, perm) // same as old Open
Open(name) // same as old Open(name, O_RDONLY, 0)
Create(name) // same as old Open(name, O_RDWR|O_TRUNC|O_CREAT, 0666)

This CL includes a gofix module and full code updates: all.bash passes.
(There may be a few comments I missed.)

The interesting packages are:
        gofix
        os
Everything else is automatically generated except for hand tweaks to:
        src/pkg/io/ioutil/ioutil.go
        src/pkg/io/ioutil/tempfile.go
        src/pkg/crypto/tls/generate_cert.go
        src/cmd/goyacc/goyacc.go
        src/cmd/goyacc/units.y

R=golang-dev, bradfitzwork, rsc, r2
CC=golang-dev
https://golang.org/cl/4357052

src/pkg/net/parse.go

@@ -63,7 +63,7 @@ func (f *file) readLine() (s string, ok bool) {
 }
 
 func open(name string) (*file, os.Error) {
-	fd, err := os.Open(name, os.O_RDONLY, 0)
+	fd, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}