try to force ctrace for the outer core

Author: nedbat

igor.py

@@ -191,6 +191,7 @@ def run_tests_with_coverage(core, *runner_args):
     import coverage
 
     cov = coverage.Coverage(config_file="metacov.ini")
+    cov.set_option("run:core", "ctrace")
     cov._warn_unimported_source = False
     cov._warn_preimported_source = False
     cov._metacov = True

metacov.ini

@@ -8,6 +8,7 @@
 
 [run]
 branch = true
+core = ctrace
 data_file = ${COVERAGE_METAFILE-.metacov}
 disable_warnings = no-sysmon
 parallel = true