Reduce peak memory usage of the static analyzer on sqlite3 (when using inlining) by 30%.

This is accomplished by periodically reclaiming nodes in the graph.  This was an optimization
done before the CFG was linearized, but the CFG linearization destroyed that optimization since each
freshly created node couldn't be reclaimed and we only looked at a window of nodes created between
each ProcessStmt.  This optimization can be reclaimed my merely expanding the window to N number of nodes.

llvm-svn: 148888