Revert "Fix DateTime subtraction"

This reverts commit 9a5d7fa6c21e3e22025ed981070f561d9c71cc03.
Fix problem with operator replacements

FunScript.Quote.specialOp was not getting the parameter types into
account when getting the method info, and because of this it was failing
when the type had overloaded operators.
Merge pull request #135 from alfonsogarciacaro/master

Fix problem with operator replacements