findGlobals() does not acknowledge when expression attaches packages via library() etc.

`findGlobals()` does not acknowledge when expression attaches packages via `library()` etc, e.g.

``` r
> library(globals)
> findGlobals(substitute({ globals::getGlobals }, env=list()))
[1] "::" "{"
> findGlobals(substitute({ getGlobals }, env=list()))
[1] "{" "getGlobals"
> findGlobals(substitute({ library(globals); getGlobals }, env=list()))
[1] "{" "getGlobals" "library"
```

In case someone wonders about `library()`;

``` r
> codetools::findGlobals(function() { library(globals); getGlobals })
[1] "{" "getGlobals" "library"

> globals::findGlobals({ library(globals); getGlobals }, substitute=TRUE)
[1] "{" "getGlobals" "library"

> library(globals)
> g <- getGlobals({ library(globals); getGlobals }, substitute=TRUE)
> g <- cleanup(g)
> str(g)
List of 1
$ getGlobals:function (expr, envir = parent.frame(), ..., method = c("conservative",
"liberal"), tweak = NULL, substitute = FALSE, mustExist = TRUE, unlist = TRUE)
- attr(*, "class")= chr [1:2] "Globals" "list"
> environment(g$getGlobals)

```

Start by inspecting the implementation and tests for findGlobals(), then run the reproducing expressions shown in the issue, including library(globals) followed by getGlobals. Done means the result acknowledges the attached package so getGlobals is resolved rather than reported as a global, while preserving the existing behavior for the other examples.

Written by the indexing model from the issue text.