Make the freed-block-queue volume metrics 64-bit throughout, to avoid

Make the freed-block-queue volume metrics 64-bit throughout, to avoid
any wierdness on very large machines in the future.  Also, double the
default size from 5MB to 10MB, on the basis that programs are now on
average twice as lardy as they were when it was set to 5MB, whenever
that was.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@7256