[release-branch.go1] misc/vim: fix for autocompletion

[release-branch.go1] misc/vim: fix for autocompletion

««« backport 7fb0e868dc39
misc/vim: fix for autocompletion

    Vim autocompletion respects the $GOPATH variable and does not
    ignore dashes ('-'), dots ('.') and underscores ('_') like found
    in many remote packages.
    Environment variable $GOROOT is determined by calling
    'go env GOROOT' instead of relying on the user's environment
    variables.

    Fixes #3876
    Fixes #3882

R=golang-dev, franciscossouza, dsymonds, minux.ma
CC=golang-dev
https://golang.org/cl/6443151

»»»