Ignore '.trs' files

When doing checks with automake, there are '<testname>.trs' files left
behind, that might or might not be usable, however these show up in
'git status' even though we definitely don't want them to be tracked
in the repository'.  Automake adds the '--trs-files' option by default
since commit 0c81b43f711fb861f04227ced8dba889596d9c43 [1], which
consequently (from 1.13 in my case) started leaving these files behind
along with '<testname>.log' files as well (which we already ignore).

[1] http://git.savannah.gnu.org/gitweb/?p=automake.git;a=commitdiff;h=0c81b43

.gitignore

@@ -134,6 +134,7 @@
 /src/virtlockd.init
 /tests/*.log
 /tests/*.pid
+/tests/*.trs
 /tests/*xml2*test
 /tests/commandhelper
 /tests/commandtest