Sentinel test: jump to next unit on test failure.

Sentinel tests are designed to be dependent on the previous tests in the
same unit, so usually we can't continue with the next test in the same
unit if a previous test failed.

tests/sentinel.tcl

@@ -145,6 +145,8 @@ proc test {descr code} {
             set msg [string range $error 10 end]
             puts [colorstr red $msg]
             if {$::pause_on_error} pause_on_error
+            puts "(Jumping to next unit after error)"
+            return -code continue
         } else {
             # Re-raise, let handler up the stack take care of this.
             error $error $::errorInfo