Variety of improvements

- Rename sources to distfiles for clarity.
- Per sys(a/c) distfiles to reduce rootfs.py processing and reduce RAM
  usage in sysa.
- Canonicalise early kaem mes/tcc files to kaem script conventions.
- Cleanup unused setup in python.

sysc/run2.sh

@@ -9,6 +9,7 @@
 
 set -e
 
+# shellcheck disable=SC2153
 trap 'env - PATH=${PREFIX}/bin PS1="\w # " bash -i' EXIT
 
 # shellcheck source=sysa/helpers.sh