test harness: Tweak quiet-test output

- Print the test name and data after the plan line

- Split on the plan line rather than on comments

  + That makes tap-filter more suitable to filter TAP output generated by other
    TAP producers.

  + However, the filtered output deletes the plan line and adds a blank line in
    its stead.  This suits our use-case of interactive test runs.

tests/tap-filter

@@ -41,5 +41,7 @@ use strict;
 undef $/; # slurp mode
 print for
   grep { /^ok.*# TODO/m or /^not ok(?!.*# TODO)/m or /^Bail out!/m }
-    split /^(?=#)/m,
+    # Split on plan lines and remove them from the output.  (To keep them,
+    # use the lookahead syntax, «(?=…)», to make the match zero-length.)
+    split /^\d+\.\.\d+$/m,
       <STDIN>;