Make DEBUG command handle "f" flag.

man/remind.1

@@ -3049,7 +3049,7 @@ under program control.  The format is:
 .PP
 \fBDEBUG\fR [+\fIflagson\fR] [\-\fIflagsoff\fR]
 .PP
-\fIFlagson\fR and \fIflagsoff\fR consist of strings of the characters "extvl"
+\fIFlagson\fR and \fIflagsoff\fR consist of strings of the characters "extvlf"
 that correspond to the debugging options discussed in the command-line
 options section.  If preceded with a "+", the corresponding group of
 debugging options is switched on.  Otherwise, they are switched off.

src/main.c

@@ -863,6 +863,11 @@ int DoDebug(ParsePtr p)
 	    else     DebugFlag &= ~DB_PRTLINE;
 	    break;
 
+	case 'f':
+	case 'F':
+	    if (val) DebugFlag |= DB_TRACE_FILES;
+	    else     DebugFlag &= ~DB_TRACE_FILES;
+	    break;
 	}
     }
 }