Use qualified name at::Half in Dispatch.h

This makes AT_DISPATCH_ALL_TYPES_AND_HALF valid outside of the at
namespace.

See pytorch/extension-cpp#15

Author: colesbury

aten/src/ATen/Dispatch.h

@@ -17,7 +17,7 @@
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Double, double, __VA_ARGS__)       \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Float, float, __VA_ARGS__)         \
       default:                                                                \
-        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'"); \
+        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'");  \
     }                                                                         \
   }()
 
@@ -29,7 +29,7 @@
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Float, float, __VA_ARGS__)         \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Half, Half, __VA_ARGS__)           \
       default:                                                                \
-        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'"); \
+        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'");  \
     }                                                                         \
   }()
 
@@ -43,7 +43,7 @@
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Long, int64_t, __VA_ARGS__)        \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Short, int16_t, __VA_ARGS__)       \
       default:                                                                \
-        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'"); \
+        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'");  \
     }                                                                         \
   }()
 
@@ -59,7 +59,7 @@
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Long, int64_t, __VA_ARGS__)        \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Short, int16_t, __VA_ARGS__)       \
       default:                                                                \
-        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'"); \
+        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'");  \
     }                                                                         \
   }()
 
@@ -74,8 +74,8 @@
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Int, int32_t, __VA_ARGS__)         \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Long, int64_t, __VA_ARGS__)        \
       AT_PRIVATE_CASE_TYPE(at::ScalarType::Short, int16_t, __VA_ARGS__)       \
-      AT_PRIVATE_CASE_TYPE(at::ScalarType::Half, Half, __VA_ARGS__)           \
+      AT_PRIVATE_CASE_TYPE(at::ScalarType::Half, at::Half, __VA_ARGS__)       \
       default:                                                                \
-        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'"); \
+        AT_ERROR(#NAME, " not implemented for '", the_type.toString(), "'");  \
     }                                                                         \
   }()