[luatex] Allow piped input

[Henri Menke]

Dear devs,

It would be great if LuaTeX accepted piped input.  Currently a command
like

    texlua <(echo 'print "Hello"')

fails with an error like "Script file /dev/fd/63 not found".  I have
attached a simple patch which would eliminate the failure.

Cheers, Henri

diff --git a/source/texk/web2c/luatexdir/lua/luainit.c b/source/texk/web2c/luatexdir/lua/luainit.c
index 7abf8c8ee..2706c5fd6 100644
--- a/source/texk/web2c/luatexdir/lua/luainit.c
+++ b/source/texk/web2c/luatexdir/lua/luainit.c
@@ -513,7 +513,7 @@ static void parse_options(int ac, char **av)
 */
 
 #define is_readable(a) (stat(a,&finfo)==0) \
-    && S_ISREG(finfo.st_mode) \
+    && (S_ISREG(finfo.st_mode) || S_ISFIFO(finfo.st_mode)) \
     && (f=fopen(a,"r")) != NULL && !fclose(f)
 
 static char *find_filename(char *name, const char *envkey)