Renamed the target to 'libvirt' and added 'product_prefix' to match the
definition in src/node_libvirt.cc's NODE_MODULE. This fixes a problem building
and using the module using newer versions of node (0.10.5). Also updated
the 'main' path in the package.json.
Merge pull request #20 from dohpaz42/v0.10.5

Fixes to get node-libvirt working on newer versions of node.js (v0.10.5)
When using libvirt 1.0.5 (maybe earlier, not sure), and an exception is
thrown from the node-libvirt, trying to inspect the "str3" property of
the exception causes a segmentation fault 11 in node. This patches that
problem by first ensuring the "str3" symbol is not null before passing
it to v8::String::New, and adds the same guards to the "str1" and "str2"
symbols as well as a precaution.
Merge branch 'segfault-error-str3'

* segfault-error-str3:
  When using libvirt 1.0.5 (maybe earlier, not sure), and an exception is thrown from the node-libvirt, trying to inspect the "str3" property of the exception causes a segmentation fault 11 in node. This patches that problem by first ensuring the "str3" symbol is not null before passing it to v8::String::New, and adds the same guards to the "str1" and "str2" symbols as well as a precaution.