Task Server

- Added 'taskd.server' and 'taskd.credentials' as supported configuration
  variables.
- Added the 'taskd.server' values to the 'diagnostics' command output.
- Updated taskrc.5.in to mention the new variables.

src/commands/CmdShow.cpp

@@ -180,6 +180,8 @@ int CmdShow::execute (std::string& output)
     " shadow.notify"
     " shell.prompt"
     " tag.indicator"
+    " taskd.server"
+    " taskd.credentials"
     " undo.style"
     " urgency.active.coefficient"
     " urgency.annotations.coefficient"