Scheduler rename

• Adds strings to scheduling language (though with a very limited character set, there are no special symbols except _, -, and spaces; basically this is intended as strings that are reasonable for function names and file names).
• Adds a rename pass which allows us to rename functions to avoid having to access pass results using generated function names.

juno_samples/fork_join_tests/src/cpu.sch

@@ -14,6 +14,8 @@ cpu(auto.test5);
 cpu(auto.test7);
 cpu(auto.test8);
 
+let test1_cpu = auto.test1;
+rename["test1_cpu"](test1_cpu);
 
 ip-sroa(*);
 sroa(*);
@@ -39,7 +41,10 @@ dce(*);
 fixpoint panic after 20 {
   infer-schedules(*);
 }
-fork-split(auto.test1);
+
+let out = fork-split(test1_cpu);
+let first_fork = out.test1_cpu.fj1;
+
 fixpoint panic after 20 {
   unroll(auto.test1);
 }