Initialize v8 platform as needed

See http://comments.gmane.org/gmane.comp.lang.javascript.v8.general/8029
for more information.
Remove stray debug-echo
Include libplatform.h only for v8 >= 3.29.36
Merge pull request #105 from stesie/fix-init-platform

Call V8::InitializePlatform as needed, fixes builds >= 3.29.36