Fail script if command fails

Use the Bash `set -e` option to make the test script fail if a command
fails. While we are at it add sanity check commands that call the
compiler and `cargo`.

Author: tcharding

contrib/test.sh

@@ -1,5 +1,7 @@
 #!/bin/sh -ex
 
+set -e
+
 FEATURES="compiler use-serde rand"
 
 # Use toolchain if explicitly specified
@@ -8,6 +10,9 @@ then
     alias cargo="cargo +$TOOLCHAIN"
 fi
 
+cargo --version
+rustc --version
+
 # Format if told to
 if [ "$DO_FMT" = true ]
 then