patch 8.2.1640: Amiga: missing header for getgrgid()

Problem:    Amiga: missing header for getgrgid().
Solution:   Add the grp.h header. (Ola Söder, closes #6906)

src/os_amiga.h

@@ -91,6 +91,7 @@ typedef long off_t;
 # include <limits.h>
 # include <errno.h>
 # include <pwd.h>
+# include <grp.h>
 # include <dirent.h>
 #endif
 

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1640,
 /**/
     1639,
 /**/