mm(1): fixes bug with -a; mm.1, tests/mm.mk: changes to test regression in -a and -t

docs/mm.1

@@ -4,7 +4,7 @@
 .\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
 .\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
 .\"
-.TH MM 1 2024-07-14 "Harakit X.X.X"
+.TH MM 1 2025-11-01 "Harakit X.X.X"
 .SH NAME
 mm \(en middleman
 .\"
@@ -22,7 +22,9 @@ Catenate input files and write them to the start of each output file or stream.
 .SH OPTIONS
 
 .IP \fB-a\fP
-Opens outputs for appending rather than updating.
+Opens outputs for appending rather than updating. Implies the
+.B -t
+option.
 .IP \fB-e\fP
 Use the standard error as an output.
 .IP \fB-t\fP
@@ -59,6 +61,10 @@ unncessary.
 .\"
 .SH HISTORY
 
+The \fB-t\fP option was originally the reverse functionality, as the default
+behavior was to overwrite outputs. This was deemed counterintuitive and the
+default behavior was changed.
+
 This utility originally had a \fB-u\fP option for compatibility with cat(1p),
 but this option is almost always default behavior in practice; therefore, it
 was dropped both for simplicity and to expand the