Fix buffer overflow in strcpy

The string needs space for the terminating null as well. This did not cause trouble on Linux, probably because nothing got broken thanks to the memory layout. OS X is less forgiving when it comes to buffer overflows and terminated the program with an abort signal.

@mtuckerman, do you suspect there might be more place where this is an issue? I only found cases where a string of length `MAXWORD` is allocated dynamically - those are very likely fine.

With this fix, PINY seems to run on OS X just fine.