Fix problem introduced on Windows that enabled vc when it shouldn't
TLegend and TLatex.
Do not add to the headers for the pch the includes in the payload
Associate to autoParse entries only the payload (ROOT-6321)

de facto implementing lazy payload parsing instead of header
parsing on demand.
Improve autoparsing procedure

o Do autoload on autoparse and not viceversa
o Do not parse headers at module registration but rather the payload
  if not in lazy payload parsing mode
o Add a barrier not to re-parse payloads: fatal in presence of Aclic
libs or various missing include guards
Make sure that the list of bases is complete.
Clean & modernise  method for source code generation
Do not parse rootlogon (ROOT-4394).