minor cleanup, no functional change:

minor cleanup, no functional change:
* in node type switches, explicitly handle all types, sort them,
and abort() on those that cannot occur
* avoid testing pointers as truth values, use "!= NULL"
* avoid testing "constant == variable", use "variable == constant"
* prefer sizeof(var) over sizeof(type)
* delete one duplicate function
* sort some declarations
* delete some useless blank lines