Previously 'load-thunk-from-memory' would often throw to 'system-error'
when passed an incorrect ELF file, leading to incorrect error messages.
* libguile/loader.c (load_thunk_from_memory): Reset 'errno' when
'check_elf_header' returns non-NULL.
* test-suite/tests/vm.test: New file.
* test-suite/Makefile.am (SCM_TESTS): Add it.
