Fix rbvmomi name[0] for ruby 1.8.7

In ruby 1.9 string index 0 returns a char, where in 1.8.7 this returns
the ascii value. This fixs the issue in Ruby 1.8.7.
Merge pull request #10 from nanliu/tb/18fix

Fix rbvmomi name[0] for ruby 1.8.7