Extend pigz option parser with simple support for '--' option list
terminator to make it syntax-compatible with GNU gzip.

(c) 2010 Michał Górny <gentoo@mgorny.alt.pl>

diff -dupr pigz-2.1.6.orig//pigz.c pigz-2.1.6/pigz.c
--- pigz-2.1.6.orig//pigz.c	2010-04-03 14:11:13.929950502 +0200
+++ pigz-2.1.6/pigz.c	2010-04-03 14:16:50.766949317 +0200
@@ -2914,6 +2914,7 @@ local size_t num(char *arg)
 local int option(char *arg)
 {
     static int get = 0;     /* if not zero, look for option parameter */
+    static char ddash = 0;  /* if not zero, we got '--' and option parsing should stop */
     char bad[3] = "-X";     /* for error messages (X is replaced) */
 
     /* if no argument or dash option, check status of get */
@@ -2923,6 +2924,8 @@ local int option(char *arg)
     }
     if (arg == NULL)
         return 0;
+    if (ddash)
+        return 1;
 
     /* process long option or short options */
     if (*arg == '-') {
@@ -2935,6 +2938,12 @@ local int option(char *arg)
             int j;
 
             arg++;
+            /* stop parsing options after '--' */
+            if (*arg == 0) {
+                ddash++;
+                return 0;
+            }
+
             for (j = NLOPTS - 1; j >= 0; j--)
                 if (strcmp(arg, longopts[j][0]) == 0) {
                     arg = longopts[j][1];