MSG_OUT strings longer than 200 characters are truncated

[MalcolmCurrie]

When fixing Issue 71, I noticed that although MSG__SZMSG is 300, if I set
the terminal width to greater than 200 characters, the list of values reported by
HDSTRACE was truncated to 200 characters.

I found that changing EMS__SZTOK in ems_par.h to be 300 cured the
problem. However, I'm not familiar enough with EMS and MERS code to
determine where this takes effect (although I did a little exploration), and hence
whether or not it's a bug elsewhere (say using the wrong global constant to
declare a character-string variable), or if this edit would have any side effects.