tests/smoke.tst: Check that --help and --version don't produce
output on stderr.
tests/smoke.tst: Add regression test for aven segfault when used on
a system set to use a language which aven doesn't support (this bug
was fixed some time ago, but we want to ensure it doesn't reappear).
NEWS: Correct "SURVEX_LANG" to "SURVEXLANG" in old NEWS entry.
NEWS: Update.