change error printing from errnum to errsym

When printing an error, calc used to print the errnum (error number):

    ; 1/0
	    Error 10001

Calc now prints the errsym (errsym):

    ; 1/0
	    Error E_DIVBYZERO

Added errsym E_LN_3 for ln(0).
Added errsym E_LOG_5 for log(0).
Added errsym E_LOG2_4 for log2(0).
Added errsym E_LOGN_6 for logn(0,base).

help/freopen

@@ -28,7 +28,7 @@ EXAMPLE
 	    "Leonard Euler"
     ; !chmod u-w /tmp/junk
     ; freopen(f, "w")
-	    Error 10013
+	    Error E_FRAC
 
 LIMITS
     none
@@ -40,7 +40,7 @@ SEE ALSO
     errno, fclose, feof, ferror, fflush, fgetc, fgetline, fgets, files, fopen,
     fprintf, fputc, fputs, fseek, fsize, ftell, isfile, printf, prompt
 
-## Copyright (C) 1999-2006,2021  Landon Curt Noll
+## Copyright (C) 1999-2006,2021,2023  Landon Curt Noll
 ##
 ## Calc is open software; you can redistribute it and/or modify it under
 ## the terms of the version 2.1 of the GNU Lesser General Public License