Fix problems resulting from Rust now checking for overflow / underflow

[DaGenix]

Fix problems resulting from Rust not checking for overflow / underflow:

• Work around a Rust bug with the overflow / underflow checking as it relates to SIMD types - ICE - tried to get overflow intrinsic for non-int type rust-lang/rust#23037. When "ndebug" is NOT defined (ie: overflow checking is on), use a new "fake-SIMD" type that just simulates all of the SIMD operations using regular tuples of integer types. When "ndebug" is defined (ie: overflow checking is off), use the regular SIMD types.
• Replace all addition, subtraction, and multiplication that was causing test failures due to overflowing or underflowing with wrapped_add(), wrapped_sub(), or wrapped_mul() as appropriate.
• Disable optimizations for test builds to help try to make sure that no more overflowing or underflowing operations make it into the code base without using the wrapped_* functions.

Closes #266