check / test inlining of list operations

[lrytz]

with the latest heuristics (not yet merged):

• when compiling all of the library, mapConserve has its loop method inlined, but dropWhile has a call to loop$3
• when only compiling (re-compiling) List.scala, both methods have their loop methods inlined

this is relevant because dropWhile cannot be inlined into other classfiles if it contains a call to loop$3, that method is not public.