Clarify types of errors in spec text (#385)

* Clarify types of errors in spec text

* Update Section 5 -- Validation.md

spec/Section 3 -- Type System.md

@@ -308,7 +308,7 @@ the built-in scalar types should be omitted for brevity.
 
 A GraphQL server, when preparing a field of a given scalar type, must uphold the
 contract the scalar type describes, either by coercing the value or
-producing an error.
+producing a field error.
 
 For example, a GraphQL server could be preparing a field with the scalar type
 `Int` and encounter a floating-point number. Since the server must not break the
@@ -1263,7 +1263,7 @@ type of an Object or Interface field.
 **Input Coercion**
 
 The value for an input object should be an input object literal or an unordered
-map supplied by a variable, otherwise an error must be thrown. In either
+map supplied by a variable, otherwise a query error must be thrown. In either
 case, the input object literal or unordered map must not contain any entries
 with names not defined by a field of this input object type, otherwise an error
 must be thrown.

spec/Section 5 -- Validation.md

@@ -973,9 +973,9 @@ referenced.
 
 **Explanatory Text**
 
-Named fragment spreads must refer to fragments defined
-within the document. If the target of a spread is
-not defined, this is an error:
+Named fragment spreads must refer to fragments defined within the 
+document. It is a validation error if the target of a spread is
+not defined.
 
 ```graphql counter-example
 {

spec/Section 6 -- Execution.md

@@ -716,5 +716,6 @@ resolves to {null}, then the entire list must resolve to {null}.
 If the `List` type is also wrapped in a `Non-Null`, the field error continues
 to propagate upwards.
 
-If all fields from the root of the request to the source of the error return
-`Non-Null` types, then the {"data"} entry in the response should be {null}.
+If all fields from the root of the request to the source of the field error
+return `Non-Null` types, then the {"data"} entry in the response should
+be {null}.

spec/Section 7 -- Response.md

@@ -6,7 +6,7 @@ operation if successful, and describes any errors encountered during the
 request.
 
 A response may contain both a partial response as well as encountered errors in
-the case that an error occurred on a field which was replaced with null.
+the case that a field error occurred on a field which was replaced with null.
 
 
 ## Serialization Format