imports: print dir of candidates in addition to import path

The import path is ambiguous in the presence of vendoring (e.g. golang/go#20610)

Change-Id: I22f372b233b8554e3d9210b383a7df7a6a0f3eee
Reviewed-on: https://go-review.googlesource.com/53470
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

imports/fix.go

diff --git a/imports/fix.go b/imports/fix.go
index ac7f4b0..e246084 100644
--- a/imports/fix.go
+++ b/imports/fix.go
@@ -776,7 +776,7 @@
 	sort.Sort(byImportPathShortLength(candidates))
 	if Debug {
 		for i, pkg := range candidates {
-			log.Printf("%s candidate %d/%d: %v", pkgName, i+1, len(candidates), pkg.importPathShort)
+			log.Printf("%s candidate %d/%d: %v in %v", pkgName, i+1, len(candidates), pkg.importPathShort, pkg.dir)
 		}
 	}