bug#13445: add2rline usage in manual

[Paul Eggert]

With newer addr2line, -p is helpful because function names
aren't printed without it.  In trunk bzr 111564..5 I pushed the
following, to suggest -p if available and to say what to do with
older addr2line implementations.

=== modified file 'doc/emacs/ChangeLog'
--- doc/emacs/ChangeLog 2013-01-19 20:38:13 +0000
+++ doc/emacs/ChangeLog 2013-01-19 22:10:50 +0000
@@ -1,3 +1,10 @@
+2013-01-19  Paul Eggert  <eggert@cs.ucla.edu>
+
+       * trouble.texi (Crashing): Suggest -p for recent addrline.  (Bug#13445)
+       Without it, I don't see function names.  Older addrlines will die
+       out sooner or later, so tailor the suggestion to recent addrline
+       and put in a comment about older ones.
+
 2013-01-19  Glenn Morris  <rgm@gnu.org>
 
        * custom.texi (Directory Variables): Fix paren typo.

=== modified file 'doc/emacs/trouble.texi'
--- doc/emacs/trouble.texi      2013-01-19 20:38:13 +0000
+++ doc/emacs/trouble.texi      2013-01-19 22:14:42 +0000
@@ -325,7 +325,8 @@
 
 @example
 sed -n 's/.*\[\(.*\)]$/\1/p' @var{backtrace} |
-  addr2line -C -f -i -e @var{bindir}/@var{emacs-binary}
+  addr2line -C -f -i -p -e @var{bindir}/@var{emacs-binary}
+# Omit '-p' for binutils 2.20 and earlier.
 @end example
 
 @noindent