pipes: stop printing an error when pipes close

Fixes #156

icdiff

@@ -736,3 +736,8 @@ if __name__ == "__main__":
             pass
         else:
             raise
+    # Close stderr to prevent printing errors when icdiff is piped to
+    # something that closes before icdiff is done writing
+    #
+    # See: https://stackoverflow.com/questions/26692284/how-to-prevent-brokenpipeerror-when-doing-a-flush-in-python
+    sys.stderr.close()

test.sh

@@ -121,6 +121,12 @@ check_gold gold-subcolors-bad-cat tests/input-{1,2}.txt --cols=80 --color-map='c
 check_gold gold-subcolors-bad-fmt tests/input-{1,2}.txt --cols=80 --color-map='change:magenta:gold,description:cyan_bold'
 check_gold gold-bad-encoding.txt tests/input-{1,2}.txt --encoding=nonexistend_encoding
 
+# Testing pipe behavior doesn't fit well with the check_gold system
+$INVOCATION tests/input-{4,5}.txt 2>/tmp/icdiff-pipe-error-output | head -n 1
+if [ -s /tmp/icdiff-pipe-error-output ]; then
+  echo 'emitting errors on early pipe closure'
+  fail
+fi
 
 VERSION=$($INVOCATION --version | awk '{print $NF}')
 if [ "$VERSION" != $(head -n 1 ChangeLog) ]; then