isTopLevelEnv: Determine if an environment is a top level environment
Description
Here, we define that as .GlobalEnv, any namespace, emptyenv,
or baseenv. This is useful to determine the effective size
of an R function, due to R including the objects from enclosing
environments
Usage
isTopLevelEnv(x)
Value
A logical. FALSE if it is not one of the "Top Level Environments",
TRUE otherwise.