Customize 'permission denied' error.

Add Fedora-specific message to error output when dumpcap cannot be started
because of permissions.

diff --git a/capture_sync.c b/capture_sync.c
index 8c49ed2..65e242d 100644
--- a/capture_sync.c
+++ b/capture_sync.c
@@ -368,6 +368,7 @@ sync_pipe_start(capture_options *capture_opts, capture_session *cap_session)
     gchar *signal_pipe_name;
 #else
     char errmsg[1024+1];
+    const char *securitymsg = "";
     int sync_pipe[2];                       /* pipe used to send messages from child to parent */
     enum PIPES { PIPE_READ, PIPE_WRITE };   /* Constants 0 and 1 for PIPE_READ and PIPE_WRITE */
 #endif
@@ -638,8 +639,10 @@ sync_pipe_start(capture_options *capture_opts, capture_session *cap_session)
         dup2(sync_pipe[PIPE_WRITE], 2);
         ws_close(sync_pipe[PIPE_READ]);
         execv(argv[0], argv);
-        g_snprintf(errmsg, sizeof errmsg, "Couldn't run %s in child process: %s",
-                   argv[0], g_strerror(errno));
+        if (errno == EPERM || errno == EACCES)
+            securitymsg = "\nAre you a member of the 'wireshark' group? Try running\n'usermod -a -G wireshark _your_username_' as root.";
+        g_snprintf(errmsg, sizeof errmsg, "Couldn't run %s in child process: %s%s",
+            argv[0], g_strerror(errno), securitymsg);
         sync_pipe_errmsg_to_parent(2, errmsg, "");
 
         /* Exit with "_exit()", so that we don't close the connection
@@ -731,6 +734,7 @@ sync_pipe_open_command(char** argv, int *data_read_fd,
     PROCESS_INFORMATION pi;
 #else
     char errmsg[1024+1];
+    const char *securitymsg = "";
     int sync_pipe[2];                       /* pipe used to send messages from child to parent */
     int data_pipe[2];                       /* pipe used to send data from child to parent */
 #endif
@@ -865,8 +869,10 @@ sync_pipe_open_command(char** argv, int *data_read_fd,
         ws_close(sync_pipe[PIPE_READ]);
         ws_close(sync_pipe[PIPE_WRITE]);
         execv(argv[0], argv);
-        g_snprintf(errmsg, sizeof errmsg, "Couldn't run %s in child process: %s",
-                   argv[0], g_strerror(errno));
+        if (errno == EPERM || errno == EACCES)
+            securitymsg = "\nAre you a member of the 'wireshark' group? Try running\n'usermod -a -G wireshark _your_username_' as root.";
+        g_snprintf(errmsg, sizeof errmsg, "Couldn't run %s in child process: %s%s",
+            argv[0], g_strerror(errno), securitymsg);
         sync_pipe_errmsg_to_parent(2, errmsg, "");
 
         /* Exit with "_exit()", so that we don't close the connection