Preserve binary data when copying file streams

Copy the bytes returned by fread instead of treating each input chunk as a NUL-terminated string. Preserve the public stream positions and report read and write failures rather than returning success after a partial copy. Add binary boundary, current-position, native pipe error and full-device regression coverage.

test/Makefile.am

@@ -19,6 +19,7 @@ clean-local:
 TESTS           =
 TESTS          += chomp
 TESTS          += copyfile
+TESTS          += fcopyfile
 TESTS          += dir
 TESTS          += fexist
 TESTS          += fisdir