remove some consts in the function arg declarations

These functions take const in OpenSSL 1.0.0+ but not in 0.9.8. Removing
the const declaration will silence warnings for 0.9.8 but not cause them
in 1.0.0+. Not ideal, but *fingers crossed* shouldn't cause problems
Merge pull request #368 from reaperhulk/more-warnings-fixes

Remove some consts in the function arg declarations