Audit file handling code

[takkaria]

• allocate all pathnames dynamically (no buffer-too-short problems)
• all pathnames should always be stored system-specific and absolute (and so only one place needs filename translation)
• init font/graf/sound directories globally at the beginning
• see if we can't design a single API that encompasses both fd_open() and my_fopen() and then switch to just use the one interface