Make replacement of ##s consistent when drawing formats, whether

followed by [ or not. Add a flag (e) to the q: format modifier to double
up #s and use it for the window_flags format variable so it doesn't end
up escaping any following text. GitHub issue 2485.

tmux.1

@@ -4638,7 +4638,12 @@ of the variable respectively.
 .Ql q:\&
 will escape
 .Xr sh 1
-special characters.
+special characters or with an
+.Ql e
+suffix, escape hash characters (so
+.Ql #
+becomes
+.Ql ## ).
 .Ql E:\&
 will expand the format twice, for example
 .Ql #{E:status-left}