Add SCons build support to Hall A analyzer.
Changed ROOT check to assume first that ROOTSYS definition is not
needed, and to just look for root-config in the path.  Otherwise, if
ROOTSYS happens to be defined, but root-config is not in that path, try
that to see if it works.

Added also possibility for true 64-bit build on Linux systems, if
available, and removed Windows build possibility.
Change the 'version' of the local modified version of SCons to be 4.9.9, and then
require this version in the main SConstruct file, thus hopefully ensuring use of
the locally distributed SCons package.
Fixes to 64bit/32bit architecture detection in configure scripts.
Updates to standalone codes for modern versions of gcc/g++ compilers.