compiler.cfg.utilities: move and rename the helper words block>cfg, insns>block and insns>cfg, they are useful to many testing vocabs
compiler.*: use block>cfg and insns>block in many tests instead of wordier code
splitting: new word split-indices, it's useful compiler.cfg.scheduling so let's add it to the splitting vocab too
compiler.cfg.scheduling: refactor to use split-insns and compiler.cfg.linear-scan.numbering + tests
compiler.cfg.scheduling: split-insns returns a 3-tuple instead of 3 items on the stack
compiler.cfg.dependence: more docs for the vocab
compiler.cfg.dependence/scheduling: refactoring, trying to get rid of the ugly usage of nodes dynamic variable
compiler.cfg.dependence: now the nodes are on the stack instead of being saved in a dynamic variable (fp++)
compiler.cfg.dependence.tests: unit tests for the dependence vocab
compiler.cfg.dependence: moved tree verification code to .tests

Since verify-trees just checked that make-trees worked correctly, it's
better to have that code in the test vocab instead of slowing down
every compile by running it
compiler.cfg.dependence/scheduling: more readable version of the select word
compiler.cfg.dependence/scheduling: select-parent and roots moved to scheduling

the roots stuff is only used by compiler.cfg.scheduling, so it's more
simple to have it there than in compiler.cfg.dependence
compiler.cfg.dependence: keys-for ?first is not deterministic, use tiebreak-parents to get predictable ordering
compiler.cfg.scheduling: refactoring to get rid of the roots dynamic variable
compiler.cfg.dependence/scheduling: refactoring to get rid of node's follows>>
compiler.cfg.dependence/scheduling.tests: new tests, some that doesnt work yet
compiler.cfg.dependence: node class doesn't need parent attribute, that's nice
compiler.cfg.dependence: if node subclasses identity-tuple it doesn't need the number slot
compiler.cfg.dependence/scheduling: fix(?) for #1187, just avoid shuffling ##peek...
compiler.cfg.dependence: docs