Fix function argument annotations in company-mode

[joddie]

This fixes a dumb mistake in my original patch to add company-mode support. The original patch put the whole string including return type and function name inside the parentheses. I knew that the function argument strings seemed awfully long but I couldn't figure out why .. duh.

This one strips off everything before the first open-paren when using the string as a company-mode annotation.

[dgutov]

This is better indeed. :) You also might want to rename the local var: arguments -> prototype.

[joddie]

Good point, thanks.