[Bug-apl] UserFunction_header::remove_duplicate_local_var

[Kevin Anderson]

Suggest:
    while(pos < local_vars.size(); ++pos) {        if (sym == local_vars[pos]) 
{            local_vars[pos] = local_vars.back();            
local_vars.pop_back();        }    }instead of:

    for (; pos < local_vars.size(); ++pos) {        if (sym == local_vars[pos]) 
{            local_vars[pos] = local_vars.back();            
local_vars.pop_back();        }    }