added tests for more complex search path manip
fixed tests for objects in globalenv

now actually evaluating in proper environments
is.loaded_package returns false instead of error on non-packages

before would fail even when input was a potentially legitimate
object name from search list, making it useless at filtering
packages from objects on search list (or at least, annoying)
adding message on.exit when path trim fails
removed require shim since implicit in library

require calls library anyway...
Fixed tests for is.loaded_package

Non 1L character should cause errors
more comprehensive tests for attach/detach/require
cleaned up warning messages
seach path packages to keep now in variable

Also changing strategy a bit, we now only keep the paths
elements that are in the list irrespective of position
search_path_setup now returns TRUE, test update