go.tools/cmd/godex: print correct type for const/var decls
go.tools/cmd/godex: print correct type for const/var decls

The old code printed the underlying type; e.g., the type
of time.Millisecond was reported to be int64 rather than
time.Duration.

Testsuite (and corresponding tests) in progress (another CL).

LGTM=adonovan
R=adonovan, dsymonds
CC=golang-codereviews
https://codereview.appspot.com/94770045

karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,karmakaze/go.tools