Remove redundant portion of code generated for dictionaries

as now the protoclasses carry the information.
Since we do not persist the ast in form of pcms (clang pcms), we
were obliged to transfer some annotations of the decls present
at dictionary generation time in the AST to the AST at runtime
(and of course, ultimately TClass) using c++ code in the
dictionaries.
Now, with ROOT pcms and protoclasses, the information is passed w/o
the need of these constructions.
Clean the code for treating insertion of entries in kForwardDeclared state

thanks to Philippe for the suggestions.
Pass the correct parameter to GenerateTClass
Note that ResolveTypedef can lead to autoloading and autoparsing
Return success in AutoLoad if dictionary is already loaded
Fix issues pointed out in http://root.cern.ch/phpBB3/viewtopic.php?f=3&t=18299

respect conventions of the example and do not port to ROOT coding
conventions the whole code.
TProtoClass::FillTClass: get mother classes before starting to fill TClass
White space
Create a 'forward declared' TClass for unknown base class
Silence warning
Enable header parsing on demand

set to true in the TCling constructor the boolean flag which was
previously steered by the HEADER_PARSING_ON_DEMAND env variable.
Fix doc macro: declare before use, and correctly so (return type) (ROOT-6448).
From Pere: do not build the libRoot.a / static build tag roota.cxx.
Added missing help on CMAKE_BUILD_TYPE.
Protection for ROOT-6454 (copied from 5.34 patches)
Fix for ROOT-6459
Fix for ROOT-6459
Fix for ROOT-6466. Disable the unuran test if unuran is not built.
Fix for ROOT-6458
Disabled thread local storage typedefs for MAC (build problems via current
Makefile sustem) and for AIX (not tested)