Fix boolean float conversion and product warnings.

This fixes some gcc warnings such as:
```
Eigen/src/Core/GenericPacketMath.h:655:63: warning: implicit conversion turns floating-point number into bool: 'typename __gnu_cxx::__enable_if<__is_integer<bool>::__value, double>::__type' (aka 'double') to 'bool' [-Wimplicit-conversion-floating-point-to-bool]
    Packet psqrt(const Packet& a) { EIGEN_USING_STD(sqrt); return sqrt(a); }
```

Details:

- Added `scalar_sqrt_op<bool>` (`-Wimplicit-conversion-floating-point-to-bool`).

- Added `scalar_square_op<bool>` and `scalar_cube_op<bool>`
specializations (`-Wint-in-bool-context`)

- Deprecated above specialized ops for bool.

- Modified `cxx11_tensor_block_eval` to specialize generator for
booleans (`-Wint-in-bool-context`) and to use `abs` instead of `square` to
avoid deprecated bool ops.

Eigen/src/Core/arch/SSE/PacketMath.h

@@ -218,7 +218,8 @@ template<> struct packet_traits<bool> : default_packet_traits
     HasAbs2      = 0,
     HasMin       = 0,
     HasMax       = 0,
-    HasConj      = 0
+    HasConj      = 0,
+    HasSqrt      = 1
   };
 };