gerrit: add FileInfo status constants
gerrit: add FileInfo status constants

Makes it easier for users of the ListFiles() API to evaluate Status in
FileInfo objects.

Change-Id: I974fefc9ce0fc539cd678f77899630e91f68d5b9
GitHub-Last-Rev: 352dc73960c03ab86564a74a9fa7ae4039e1f44f
GitHub-Pull-Request: golang/build#14
Reviewed-on: https://go-review.googlesource.com/c/145657
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build