Y wcfs: Rename -d to -trace.fuse

Three reasons:

1) -d is not very descriptive, it's help "debug" is also too vague;
2) currently it only activates trace of FUSE exchange
3) in the next patch we are going to introduce -debug that will activate
   debugging-only features which will remain disabled on production runs
   for safety.

-> Rename -d to -trace.fuse to clarify its meaning and prepare for
   upcoming -debug.

conftest.py

 # Wendelin.core | pytest config
-# Copyright (C) 2020-2021  Nexedi SA and Contributors.
+# Copyright (C) 2020-2024  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -73,7 +73,7 @@ def pytest_configure(config):
             wcfslog = logging.getLogger('wcfs')
             wcfslog.setLevel(logging.INFO)
         # -vv  -> verbose *.py logs
-        # XXX + $WENDELIN_CORE_WCFS_OPTIONS="-d -alsologtostderr -v=1" ?
+        # XXX + $WENDELIN_CORE_WCFS_OPTIONS="-trace.fuse -alsologtostderr -v=1" ?
         if config.option.verbose > 1:
             config.inicfg['log_cli_level'] = "INFO"
 

wcfs/wcfs.go

@@ -2892,7 +2892,7 @@ func main() {
 }
 
 func _main() (err error) {
-	debug := flag.Bool("d", false, "debug")
+	tracefuse := flag.Bool("trace.fuse", false, "trace FUSE exchange")
 	autoexit := flag.Bool("autoexit", false, "automatically stop service when there is no client activity")
 	pintimeout := flag.Duration("pintimeout", 30*time.Second, "clients are killed if they do not handle pin notification in pintimeout time")
 
@@ -2909,7 +2909,7 @@ func _main() (err error) {
 	}
 
 	// debug -> precise t, no dates	(TODO(?) -> always precise t?)
-	if *debug {
+	if *tracefuse {
 		stdlog.SetFlags(stdlog.Lmicroseconds)
 	}
 
@@ -3000,7 +3000,7 @@ func _main() (err error) {
 		ExplicitDataCacheControl: true,
 
 		DisableXAttrs: true,        // we don't use
-		Debug:         *debug,
+		Debug:         *tracefuse,  // go-fuse "Debug" is mostly logging FUSE messages
 
 		// Give access to zope users (that reside on a different Slappartition than WCFS)
 		AllowOther: true,