Make dc notice read and write errors on its input and output. I grepped for mentions of the strings `putc', `print', `getc', `FILE', `stdin', `stdout' and `stderr' and added calls to new error-checking functions unless it was clear from the immediately-surrounding code that the program was exiting nonzero, or would exit nonzero if the call failed. I ignored hits in lib/getopt*, which seems to pervasively ignore write errors when printing usage messages, in the hope that these were correct. I _think_ I got them all. -iwj.