build-sys: use Makevars --add-comments= to limit .pot comments

By not limiting --add-comments= via an argument, xgettext is far
too aggressive (one might say stupid) when extracting comments.
It doesn't even limit extraction to a single preceeding comment.

Here is an example showing a program source excerpt and the
resulting .pot excerpt:

 --- program source ----------------------------------------
 close (0); dup (in_fd[0]);  /* set the stdin to the in pipe */
 close (1); dup (out_fd[1]); /* set the stdout to the out pipe */
 close (2); dup (out_fd[1]); /* set the stderr to the out pipe */
 execvp (args[0], args);     /* exec gdb */
 perror (_("exec failed"));

 --- resulting .pot ----------------------------------------
 #. set the stdin to the in pipe
 #. set the stdout to the out pipe
 #. set the stderr to the out pipe
 #. exec gdb
 #: ps/stacktrace.c:28 ps/stacktrace.c:63
 msgid "exec failed"
 msgstr ""

1 files changed, 1 insertions, 1 deletions

diff --git a/po/Makevars b/po/Makevars
index 7865213..88a7408 100644
--- a/po/Makevars
+++ b/po/Makevars
@@ -8,7 +8,7 @@ subdir = po
 top_builddir = ..
 
 # These options get passed to xgettext.
-XGETTEXT_OPTIONS = --keyword=_ --keyword=N_ --keyword=P_:1,2 --no-wrap --escape --add-comments=
+XGETTEXT_OPTIONS = --keyword=_ --keyword=N_ --keyword=P_:1,2 --no-wrap --escape --add-comments=Translation
 
 # This is the copyright holder that gets inserted into the header of the
 # $(DOMAIN).pot file.  Set this to the copyright holder of the surrounding