Autotest: Fix awk script optimization

[Ralf Wildenhues]

Grmble.  I have no idea why I didn't catch this right away, but the
recent change caused tests 53 and 56 (Empty test suite and Tested
programs) to fail.  Applying this fix.

Sorry,
Ralf

2007-11-23  Ralf Wildenhues  <address@hidden>

        * lib/autotest/general.m4 (AT_INIT): For awk line number
        extraction script, ensure `$at_group' has a defined value
        even for the empty set, and properly quote its usage inside
        the awk script.

diff --git a/lib/autotest/general.m4 b/lib/autotest/general.m4
index b40db8d..6fa3f2e 100644
--- a/lib/autotest/general.m4
+++ b/lib/autotest/general.m4
@@ -873,7 +873,7 @@ else
 fi
 
 # Get the last needed group.
-for at_group in $at_groups; do :; done
+for at_group in : $at_groups; do :; done
 
 # Extract the start and end lines of each test group at the tail
 # of this file
@@ -885,7 +885,7 @@ BEGIN { FS="" }
 /address@hidden:@AT_STOP_/ {
   test = substr ($ 0, 10)
   print "at_sed" test "=\"1," start "d;" NR "q\""
-  if (test == '$at_group') exit
+  if (test == "'"$at_group"'") exit
 }' "$at_myself" > "$at_test_source"
 . "$at_test_source"