[ haddock ] Documented difference between local and imported signature in state.
[ minor refactor ] Factored out common subexpression.
[ issue 1186 ] Test case (shrunk by Ulf).
[ issue 1186 ] Fixed by preserving ArgInfo in clause compiler.
[ refactor ] A use of fromMaybe.
[ clean ] Removed old, commented-out code.
[ refactor ] Merge three checks for variable pattern into one.
[ comment ] Clearer comment in clause compiler.