Fix spelling error

Cosmetic only.  No code change.
Merge pull request #2 from rpgoldman/master

A number of minor improvements

Thanks to rpgoldman!
Merge branch 'master' of https://github.com/Neronus/CL-CUDD
Tidied up the build.

Fixed some forward references by adding add-apply-functions.
Replaced some non-EQL DEFCONSTANTs with ALEXANDRIA:DEFINE-CONSTANT.
Commented out two stub definitions for ADD functions that don't appear
in the CUDD header file.