Keep the Lua-less build compiling

`cgit_abort_filters` unhooks the Lua write interposer under NO_LUA
too, where neither the hook nor its state exists, so `make NO_LUA=1`
and the default mode of `tools/release-build.sh` have not compiled
since the die path learned to take stdout back from a filter. The
suite now builds that variant into `build/nolua` and runs it, and a
`lua:` filter in such a build is refused with a message naming the
cause instead of an unknown filter type.

1 file changed, 2 insertions, 1 deletion

diff --git a/MANUAL.txt b/MANUAL.txt
index 10487a3..053bb5f 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -755,7 +755,8 @@ specification with one of these strings.
 	Executes the script using a built-in Lua interpreter. The script is
 	loaded once per execution of cgit, and may be called multiple times
 	during cgit's lifetime, making it a good choice for repeated filters
-	such as the 'email filter'. It responds to three functions:
+	such as the 'email filter'. A cgit built with NO_LUA has no interpreter
+	and refuses a filter with this prefix. It responds to three functions:
 
 	'filter_open(argument1, argument2, argument3, ...)'::
 		This is called upon activation of the filter for a particular