Avoid norm which conflicts with std::norm.
TString::SubString() is not what it seems (ROOT-6296).
Properly treat typedefs and classes contained in classes

for those we just need to fwd declare the containing class.
It is enough to trigger the incomplete type error.
Less mem leaks.
Lesson from summies: be more explicit about what "?" might mean.
Handle failure in dynlookup more gracefully (ROOT-6365).
Use the SLoc of the original Expr for better readability (ROOT-6365).
GetMissingDictionaries: change behaviour for special case:pair.

Pair is a special case and it is not checked for missing dictionary, but
it will recurse on its elements if the recurse flag is on.