bugfix: check if sys:load is called in primary process
add --eval command line option
update compile-stdlib.sh for the new --eval option
compile-stdlib.sh: remove file logging

since the compiler is starting to return better error codes on failure,
it's better to stop the logfile-by-default (although you can obviously
redirect it to a file if you want)
move tests/test.xtm to libs/core/test.xtm
WIP: improved test infrastructure