Cover transforms some binary comprehensions incorrectly

In some cases cover transforms binary comprehensions into non-working ones.
Please consider example below:
---cut---
-module(wrong_transform).
-compile(export_all).

good() ->
    << <<$,, X/binary>> || X <- [ <<"a">>, <<"b">> ]>>.

bad() ->
    << <<",", X/binary>> || X <- [ <<"a">>, <<"b">> ]>>.
---cut---

With disabled cover, outputs of this functions are equal, `bad() =:=
good()`. But if you do `cover:compile_beam/1` (see decompile.erl) it blows
with `badarg` in `bad/0` function. Meanwhile `good/0` works well.

I've patched a bit `cover.erl` to dump AST forms before and after
`cover:compile_beam/1` and found that for some reason it surrounds terms
inside of comprehension with `begin ... end` pattern. It is wrong in case
of list (I can't explain why, but it throws badarg, so I guess it is
definitely an issue :)

Also I will appreciate if someone explain me why we do need this cover's
trick with `begin .. end`.

Thank you!

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--- cover.original.erl	2015-04-08 16:44:25.000000000 +0300
+++ ../lib/tools/src/cover.erl	2015-04-08 16:42:33.000000000 +0300
@@ -1359,7 +1359,10 @@ do_compile_beam(Module,Beam,UserOptions)
 	    {error,E};
 	{raw_abstract_v1,Code} ->
             Forms0 = epp:interpret_file_attribute(Code),
+	    io:format("see ~p.*.ast", [Module]),
+	    file:write_file(atom_to_list(Module) ++ ".before.ast", io_lib:format("~p", [Forms0])),
 	    {Forms,Vars} = transform(Forms0, Module),
+	    file:write_file(atom_to_list(Module) ++ ".after.ast", io_lib:format("~p", [Forms])),
 
 	    %% We need to recover the source from the compilation
 	    %% info otherwise the newly compiled module will have