[grn, groff, troff]: Improve fatal diagnostics.

[grn, groff, troff]: Communicate better when device DESC file can't be
loaded.

* src/libs/libgroff/font.cpp (font::load_desc): Stop writing diagnostic
  to standard error.

* src/preproc/grn/main.cpp (getres):
* src/roff/troff/troff.cpp (main): Replace "sorry, I can't continue"
  fatal diagnostic with a more informative message.  Instead say
  which device's DESC file the program was trying to open, which might
  reveal a user's logic error or typo.

* src/roff/groff/groff.cpp (main): Replace "invalid device" text of
  fatal diagnostic similarly.  I think it is more helpful to indicate
  the operation that failed rather than saying the device was invalid,
  particularly since there are other ways for a device to be invalid
  even if a DESC file is found and loaded.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/preproc/grn/main.cpp b/src/preproc/grn/main.cpp
index 3a2e332a9..c4a57a49f 100644
--- a/src/preproc/grn/main.cpp
+++ b/src/preproc/grn/main.cpp
@@ -429,7 +429,8 @@ getres()
   int linepiece;
 
   if (!font::load_desc())
-    fatal("sorry, I can't continue");
+    fatal("cannot load 'DESC' description file for device '%1'",
+	  device);
 
   res = font::res;