Do cling's best at returning the currently executing file.

#included files will not be picked up as cling cannot tell where the currently running function was defined.
But it does know which file was passed to MetaProcessor::executeFunction() (e.g. via .x).
So at least store that.
This fixes the occurrences of GetCurrentMacroName() in tutorials/


git-svn-id: http://root.cern.ch/svn/root/trunk@47421 27541ba8-7e3a-0410-8455-c3a389f83636