use new logmsg and set --show in tests

Also modify `logmsg` to output additional separator lines to make the
demarcation between tests even clearer.

tests/abbr.err

@@ -1,22 +1,52 @@
+
+####################
 # Test basic add and list of __abbr1
+
+####################
 # Erasing one that doesn't exist should do nothing
 abbr --erase: No abbreviation named NOT_AN_ABBR
+
+####################
 # Adding existing __abbr1 should be idempotent
+
+####################
 # Replacing __abbr1 definition
+
+####################
 # __abbr1 -s and --show tests
+
+####################
 # Test erasing __abbr1
+
+####################
 # Ensure we escape special characters on output
+
+####################
 # Ensure we handle leading dashes in abbreviation names properly
+
+####################
 # Test that an abbr word containing spaces is rejected
 abbr --add: Abbreviation 'a b c' cannot have spaces in the word
+
+####################
 # Test renaming
+
+####################
 # Test renaming a nonexistent abbreviation
 abbr --rename: No abbreviation named __abbr6
+
+####################
 # Test renaming to a abbreviation with spaces
 abbr --rename: Abbreviation 'g h i' cannot have spaces in the word
+
+####################
 # Test renaming without arguments
 abbr --rename: Requires exactly two arguments
+
+####################
 # Test renaming with too many arguments
 abbr --rename: Requires exactly two arguments
+
+####################
 # Test renaming to existing abbreviation
 abbr --rename: Abbreviation __abbr12 already exists, cannot rename __abbr11