Set the exit status to reflect pass/fail.

For Travis compatibility, we set the exit code to non-zero when
any tests fail.

Fixes #5.

tests/urchin exit code/non zero exit code when a test fails

@@ -0,0 +1,6 @@
+../../urchin "../Counts should be kept of successes and failures./.test" > /dev/null
+case $? in
+  0) exit 8;;
+  *) exit 0;;
+esac
+

tests/urchin exit code/zero exit code when tests all pass

@@ -0,0 +1 @@
+../../urchin .test > /dev/null

urchin

@@ -111,6 +111,7 @@ urchin_go() {
   set -- $(grep -e 'passed$' "$logfile"|wc -l) $(grep -e 'failed$' "$logfile"|wc -l)
   printf '%s\n' "$1 $(plural test "$1") passed."
   printf '%s\n' "$2 $(plural test "$2") failed."
+  return "$2"
 }
 
 urchin_molly_guard() {