Add a buffer management class to replace static sized char buffers on the stack.

Also allows us to gradually convert static to dynamic sizes.

Use it in CINT7 thoughout, and in CINT5 in the places that were most urgent according to a stack usage evaluation with http://home.cern.ch/axel/stacksize.sh, i.e. in G__interpret_function only for now.

Fix the lookup's conversion vs. promotion algorithm; especially the promotion part was completely wrong. This fixes Savannah #23352.


git-svn-id: http://root.cern.ch/svn/root/trunk@24073 27541ba8-7e3a-0410-8455-c3a389f83636