Fix comments and code snippets that were making incorrect claims about
the alignment requirement of the guest state, shadow areas, and register
spill area sizes.
The size of these areas ought to be a multiple of 16 bytes.


git-svn-id: svn://svn.valgrind.org/vex/trunk@2818 8f6e269a-dfd6-0310-a8e1-e2731360e62c