go/ssa: rename some API features (incompatible change)

Rename the following exported names:
	(*Program).BuildAll → Build
	(*Program).Method   → MethodValue
	Package.Object      → Pkg
Also:
	(*Function).pkgobj  → pkg

Change-Id: Iff7e6c240ebe6786ba759278ac0daa3d66698013
Reviewed-on: https://go-review.googlesource.com/14134
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index f4c64bb..b24c195 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -45,7 +45,7 @@
 //
 type Package struct {
 	Prog    *Program               // the owning program
-	Object  *types.Package         // the type checker's package object for this package
+	Pkg     *types.Package         // the corresponding go/types.Package
 	Members map[string]Member      // all package members keyed by name (incl. init and init#%d)
 	values  map[types.Object]Value // package members (incl. types and methods), keyed by object
 	init    *Function              // Func("init"); the package's init function