fix error messages in layout.cc that print a 4-char tag

[jfkthame]

There are a bunch of messages in layout.cc that incorrectly try to print a tag by using %4s and passing (char*)&tag as the argument. To ensure no more than 4 chars are printed, they need to use %4.4s as the format.

(In addition, the messages incorrectly refer to the tag as "table", but in these cases it's not the table name, it's a subsidiary tag - script, language or feature.)

[khaledhosny]

Do you happen to know any fonts that trigger (some of) those errors?

[jfkthame]

If you load http://spectrum.ieee.org/static/interactive-the-top-programming-languages with Firefox, with the developer console open, you'll see some of those error messages being reported in the log.

[khaledhosny]

Thanks.