-b option: redirect stdout/stderr to /dev/null, better explain -b in help, update manpage, and docs

doc/manpages/xschem.1.in

@@ -39,7 +39,7 @@ Print help and exit.
 .TP
 
 .B -b, --detach
-Detach xschem from console.
+Detach xschem from console (no output and no input from console)
 .TP
 
 .B -n, --netlist
@@ -66,6 +66,10 @@ Set netlist type to Verilog.
 Execute specified tcl instructions before any other action, this can be used to change xschemrc variables.
 .TP
 
+.B --preinit <file>
+Execute specified tcl instructions before any other action and before loading xschemrc.
+.TP
+
 .B --command <tcl_cmd>
 Execute specified tcl commands after completing startup.
 .TP
@@ -74,6 +78,10 @@ Execute specified tcl commands after completing startup.
 Execute specified tcl file as a command script (perhaps with xschem  commands).
 .TP
 
+.B --diff <file>
+Show differences with given file.
+.TP
+
 .B --tcp-port <number>
 Listen to specified tcp port for client connections. (number >=1024).
 .TP

doc/xschem_man/run_xschem.html

@@ -47,7 +47,7 @@ user:~$ xschem .../xschem_library/examples/0_examples_top.sch
 usage: xschem [options] [schematic | symbol ]
 Options:
   -h  --help           Print this help.
-  -b  --detach         Detach Xschem from console and fork in the background.
+  -b  --detach         Detach Xschem from console (no output and no input from console)
   -n  --netlist        Do a netlist of the given schematic cell.
   -v  --version        Print version information and exit.
   -V  --vhdl           Set netlist type to VHDL.

src/main.c

@@ -101,7 +101,13 @@ int main(int argc, char **argv)
   }
 
 
-  if(detach) fclose(stdin);
+  if(detach) {
+    fclose(stdin);
+    #ifdef __unix__
+    freopen("/dev/null", "w", stdout);
+    freopen("/dev/null", "w", stderr);
+    #endif
+  }
   if(detach && has_x) {
     Tcl_FindExecutable(argv[0]); /* tcl stores executable name for its internal usage */
     interp = Tcl_CreateInterp(); /* create the tcl interpreter */

src/xschem.help

@@ -1,7 +1,7 @@
 usage: xschem [options] [schematic | symbol ]
 Options:
   -h  --help           Print this help.
-  -b  --detach         Detach Xschem from console and fork in the background.
+  -b  --detach         Detach Xschem from console (no output and no input from console)
   -n  --netlist        Do a netlist of the given schematic cell.
   -v  --version        Print version information and exit.
   -V  --vhdl           Set netlist type to VHDL.