Test for object existence using head request.

Use the PB head option or an HTTP HEAD request.
Trimming the version number to prevent Rails error: Malformed version number string 1.4.2-0-g61ac9d8
Using split instead of truncating
Merge pull request #120 from jacepp/version-trim

Had an issue when trying to read the Riak server's version number
Merge pull request #102 from eliaslevy/exists-using-head

Test for object existence using head request.
Merge branch 'master' into bk-remove-http

Conflicts:
	lib/riak/client/http_backend.rb