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/.gitignore

@@ -4,6 +4,7 @@
 .deps/
 /chomp
 /copyfile
+/fcopyfile
 /dir
 /fexist
 /fisdir