LDMD: Made error message on compiler execution error clearer.

It is also triggered when the compiler exits with a signal, etc.
DValue: Do not uselessly inherit from Object.
DValue: struct->class.

This is in line with an incoming upstream change making all
polymorphic structs classes, and also matches common coding
conventions.
Minor DVarValue refactoring.
Detab RTTIBuilder.
Downgraded accepts-invalid workaround error to assertion.

Bug 9268 was fixed in 2.062.
Store bools as i8.

I really hope we can refactor this to use a less leaky
abstraction later – it should at least be possible to merge
voidToI8 and i1ToI8.
Add debug info for enums.

Previously enums were reduced to the underlying type.
Now the symbolic constants can be used.
Merge pull request #386 from klickverbot/store-bool-as-i8

Store bool as i8.
More trivial upstream alignment.
Revert "Add debug info for enums."

This reverts commit 001a39642fe94b5ab482e12b7f645c74d350afd1, as
it leads to debug mode crashes in rt.lifetime and other modules.

Specifically, the type check assertion in IntegerExp::toInteger
(at expression.c:2017) is hit.
Remove unused extra argument to overload checking functions.
Also avoid i1 in TupleExp::toElem.