Allow append/subtract value with --output option

Allow to append or subtract value on avail_*output and list_*output
configuration options through --output command line switch. If value
associated to --output/-o switch starts with '+' or '-', this new value
is respectively appended or subtracted from existing configuration value.

Author: xdelaruelle

tcl/init.tcl.in

@@ -292,7 +292,27 @@ proc getConf {option {valifundef {}}} {
             # overridden value coming the command-line (already validated)
             ##nagelfar ignore Suspicious variable
             if {[info exists ::asked_$option]} {
-               set value [set ::asked_$option]
+               set askedval [set ::asked_$option]
+               # append or subtract value to existing configuration value if
+               # new value starts with '+' or '-' (for colon-separated list
+               # option only)
+               if {$valuekind eq {l} && [string index $askedval 0] in {+ -}} {
+                  set curvaluelist [split $value :]
+                  switch -- [string index $askedval 0] {
+                     + {
+                        ##nagelfar ignore Found constant
+                        appendNoDupToList curvaluelist {*}[split [string\
+                           range $askedval 1 end] :]
+                     }
+                     - {
+                        lassign [getDiffBetweenList $curvaluelist [split\
+                           [string range $askedval 1 end] :]] curvaluelist
+                     }
+                  }
+                  set value [join $curvaluelist :]
+               } else {
+                  set value $askedval
+               }
             }
 
             # convert value to its internal representation

tcl/main.tcl.in

@@ -306,9 +306,11 @@ proc parseModuleCommandArgs {topcall cmd ignerr args} {
          }
          append outputconf _output
 
-         # check option value is coherent with current sub-command
-         if {[isDiffBetweenList [split $asked_output :] [lindex\
-            $::g_config_defs($outputconf) 4]]} {
+         # check option value is coherent with current sub-command (remove
+         # append/subtract operator at the start if any)
+         if {[isDiffBetweenList [split [expr {[string index $asked_output 0]\
+            in {+ -} ? [string range $asked_output 1 end] : $asked_output}]\
+            :] [lindex $::g_config_defs($outputconf) 4]]} {
             if {!$ignerr} {
                knerror "Invalid element in value list for '$output_arg'\
                   option on $cmd sub-command\nAllowed elements are: [lindex\