Revise workspace next/prev

See the issue #1798 (http://github.com/i3/i3/issues/1798).

+workspace_next+ as-is cycles through either numbered or named workspaces,
but when it reaches the last numbered/named workspace, it only looks for
named workspaces. This commit changes it: look for named workspaces after
exhausting numbered ones, but also for numbered ones after exhausting
named ones.

Also add a test case 528-workspace-next-prev.t (numbered workspaces and named
workspaces on 2 outputs) for testing this.

testcases/t/528-workspace-next-prev.t

@@ -0,0 +1,127 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Tests whether 'workspace next' works correctly.
+#
+use List::Util qw(first);
+use i3test i3_autostart => 0;
+
+sub assert_next {
+    my ($expected) = @_;
+
+    cmd 'workspace next';
+    # We need to sync after changing focus to a different output to wait for the
+    # EnterNotify to be processed, otherwise it will be processed at some point
+    # later in time and mess up our subsequent tests.
+    sync_with_i3;
+
+    is(focused_ws, $expected, "workspace $expected focused");
+}
+
+
+my $config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+fake-outputs 1024x768+0+0,1024x768+1024+0
+EOT
+my $pid = launch_with_config($config);
+
+################################################################################
+# Setup workspaces so that they stay open (with an empty container).
+# Have only named workspaces in the 1st output and numbered + named workspaces
+# in the 2nd output.
+################################################################################
+
+sync_with_i3;
+$x->root->warp_pointer(0, 0);
+sync_with_i3;
+
+cmd 'workspace A';
+# ensure workspace A stays open
+open_window;
+
+cmd 'workspace B';
+# ensure workspace B stays open
+open_window;
+
+cmd 'workspace D';
+# ensure workspace D stays open
+open_window;
+
+cmd 'workspace E';
+# ensure workspace E stays open
+open_window;
+
+cmd 'focus output right';
+
+cmd 'workspace 1';
+# ensure workspace 1 stays open
+open_window;
+
+cmd 'workspace 2';
+# ensure workspace 2 stays open
+open_window;
+
+cmd 'workspace 3';
+# ensure workspace 3 stays open
+open_window;
+
+cmd 'workspace 4';
+# ensure workspace 4 stays open
+open_window;
+
+cmd 'workspace 5';
+# ensure workspace 5 stays open
+open_window;
+
+cmd 'workspace C';
+# ensure workspace C stays open
+open_window;
+
+cmd 'workspace F';
+# ensure workspace F stays open
+open_window;
+
+cmd 'focus output right';
+
+################################################################################
+# Use workspace next and verify the correct order.
+################################################################################
+
+# The current order should be:
+# output 1: A, B, D, E
+# output 2: 1, 2, 3, 4, 5, C, F
+
+cmd 'workspace A';
+is(focused_ws, 'A', 'back on workspace A');
+
+assert_next('B');
+assert_next('D');
+assert_next('E');
+assert_next('C');
+assert_next('F');
+assert_next('1');
+assert_next('2');
+assert_next('3');
+assert_next('4');
+assert_next('5');
+assert_next('A');
+assert_next('B');
+
+exit_gracefully($pid);
+
+done_testing;