Support for breaking before nested statements

[lexandera]

Currently a debug statement is inserted only in front of the first of the nested statements, like this:

debugCode();
foo(bar(quux()));

It should be possible to use comma-separated groups of statements in the form of (funA(), funB()) for inserting debugging calls into nested code.

After this change, the generated code would look something like this instead:

(debugCode(), foo((debugCode(), bar((debugCode(), quux())))))