enable v8plus_call to be used in any thread

*** 1,10 ****
  {
          "author": "Keith M Wesolowski <keith.wesolowski@joyent.com>",
          "name": "v8plus",
          "description": "utility environment for writing addons in C",
!         "version": "0.0.5",
          "repository": {
                  "type": "git",
                  "url": "git://github.com/wesolows/v8plus.git"
          },
          "bugs": {
--- 1,13 ----
  {
          "author": "Keith M Wesolowski <keith.wesolowski@joyent.com>",
          "name": "v8plus",
          "description": "utility environment for writing addons in C",
!         "version": "0.0.6",
!         "contributors": [
!                 "Joshua M. Clulow <jmc@joyent.com>"
!         ],
          "repository": {
                  "type": "git",
                  "url": "git://github.com/wesolows/v8plus.git"
          },
          "bugs": {