fix vendor import get ignored

[Contextualist]

I'm not sure if it should be fixed this way, but the issue is probably real. Gocode handles vendor package content correctly (i.e. the exported fields of a vendor package are all shown), but it seems to ignore vendor import. To reproduce the issue:

$GOPATH/src/github.com/a/b/
|---main.go
|---vendor/github.com/c/d/
    |---p.go

Where in main.go (# denotes the cursor position)

package main

import "github.com/c#"

The option github.com/c/d does not present in the candidates.

[nsf]

Merged as is. I don't use that feature, hence have no opinion on its correctness (weird stance frrom the point of view of a maintainer, but whateverr). Patch looks somewhat innocent.