fmsg: implement suspend in writer

This removes the requirement to call fmsg.Exit on every exit path, and enables direct use of the "log" package. However, fmsg.BeforeExit is still encouraged when possible to catch exit on suspended output.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/system/tmpfiles.go

@@ -44,7 +44,7 @@ func (t *Tmpfile) Type() Enablement {
 func (t *Tmpfile) apply(_ *I) error {
 	switch t.method {
 	case tmpfileCopy:
-		fmsg.VPrintln("publishing tmpfile", t)
+		fmsg.Verbose("publishing tmpfile", t)
 		return fmsg.WrapErrorSuffix(copyFile(t.dst, t.src),
 			fmt.Sprintf("cannot copy tmpfile %q:", t.dst))
 	default:
@@ -54,11 +54,11 @@ func (t *Tmpfile) apply(_ *I) error {
 
 func (t *Tmpfile) revert(_ *I, ec *Criteria) error {
 	if ec.hasType(t) {
-		fmsg.VPrintf("removing tmpfile %q", t.dst)
+		fmsg.Verbosef("removing tmpfile %q", t.dst)
 		return fmsg.WrapErrorSuffix(os.Remove(t.dst),
 			fmt.Sprintf("cannot remove tmpfile %q:", t.dst))
 	} else {
-		fmsg.VPrintf("skipping tmpfile %q", t.dst)
+		fmsg.Verbosef("skipping tmpfile %q", t.dst)
 		return nil
 	}
 }