GHCi :m doesn't restore default decl

GHCi should remember what the 'default' setting in force for a module is, so that after :m Foo one gets the default setting for Foo.

This means that GHC should really record the default setting in the interface file.

So this is related to the current bug that GHCi doesn't remember the original source-level imports for the module. As a result :m Foo (where Foo is a compiled module) does not produce the right top-level environment