Disable by default memory checks during event loop

  Regular checks, with a tunable frequency, of process memory were introduce as a first
  debug layer. However, they require calls to System::GetProcInfo which are particurarly
  heavy. Since by default this information is not used, it makes more sense to have it off.
Use native GDI function
Introduce new TCanvas events (keyboard arrows) + add GUI handlers
Use better QueryPointer (the one which is working on Linux...)
Implement zoom with wheel on 2D histograms
remove trailing blanks
propagate the arrow keys events.
Use (translate to) TCanvas coordinates
Warp.
Check position of parameters and args.
Un-splittability as property of data member
Exclude the content of ROOT::Meta::Selection a priori to avoid mistakes

of the users, for example combining a selection xml and a dict selection.
Express in a more convenient way the default exclusions
Express non-splittability with a comment ("||")
Introduce recursion to allow recursive template argument removal

if you have something like A<int, B<double,4, float>> you must
know how many arguments you have to skip for B in advance.
Add a factorised infrastructure for template argument name removal

and disable the functionality for not removing template arguments
which are marked to be removed but have a value different from the
default one.
Atlas does not expect this feature and some more coding is involved
since this comparison is not always trivial.
Add more error messages. Make execution faster

reshuffling if conditions.
Drops the validation of the directory name in prefetch

From Elvin:

I attached a patch which drops the validation of the directory name used for caching the prefetched blocks for the TFilePrefetching. I initially used it so that I wouldn't end up with funny names for the cache directory but the Alice guys (cc - Andrei) have some problems with this check when deploying it in production since they have various characters in the directory name which I currently don't accept.

Therefore, I completely removed this validation step and I rely on the TSystem/OS to report any errors if creating/opening the requested directory is not possible.
Remove unused var error (clang trunk did not see it!)

Remove typos
Removing some more warnings (CMake)