Add simple comparisons in formats: #{==:a,b} and #{!=:a,b} ("a" and "b"

are expanded so can compare formats). And expand the condition to
#{?a,b,c} (the "a" part) if it doesn't work as a simple lookup.

Also add FORMAT_NOJOBS flag to disable jobs in a format.

tmux.1

@@ -3397,6 +3397,21 @@ is enabled, or
 .Ql no
 if not.
 .Pp
+Simple comparisons may be expressed by prefixing two comma-separated
+alternatives by
+.Ql ==
+or
+.Ql !=
+and a colon.
+For example
+.Ql #{==,#{host},myhost}
+will be replaced by
+.Ql 1
+if running on
+.Ql myhost ,
+otherwise by
+.Ql 0.
+.Pp
 A limit may be placed on the length of the resultant string by prefixing it
 by an
 .Ql = ,