allow to specify a node type: --prop:[type:]name=value

allow to specify a node type:   --prop:[type:]name=value
where type is one of string (default), double, float, long, int, bool
Using only the first letter works, too.

  --prop:foo=123         ... sets property foo to string 123 (old behavior)
  --prop:string:foo=123  ... verbose version of above
  --prop:s:foo=123       ... slightly less verbose version of above
  --prop:bool:foo=1      ... makes property a bool of value 'true'

I hope this isn't considered a silly gimmick. I need this often and maybe
other developers do, too. It's useful in cases where the difference really
matters. if (getprop("/foo")), for instance, is TRUE even when the property
contains string "false", as all strings are TRUE.