tcnksm/go-gitconfig — pull request #2 by doloopwhile (2014-09-17 04:49:09+00:00)
Title: Return ErrNotFound if value is not found

I modified functions to return the fixed error `ErrNotFound`.
It let us know whether `git config` unexpectedly aborted or just entry not found as following:
```go
v, err := gitconfig.Global("diff.tool")
if err == gitconfig.ErrNotFound {
println("diff.tool not configured, use /usr/bin/diff command")
v = "/usr/bin/diff"
}
```