Make the error message more accurate for an invalid map key type.

Change-Id: I7010cacfb7bfa47a55ae88c25849e5c0073f3636

com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties

diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
index 1357817..4bdeb24 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
@@ -11,7 +11,7 @@
 fieldNumbersMustBePositive = Field numbers must be positive integers.
 importingUnsupportedSyntax = Importing unsupported file (directly or indirectly.) This may cause errors related to unresolved references.
 importNotFound = Import \"%s\" was not found.
-invalidMapKeyType = Key in a map field cannot be of float, double, bytes or message type.
+invalidMapKeyType = Key in a map field must be of integral or string type.
 invalidMapValueType = Value in a map field cannot be a map.
 literalNotInEnum = Enum type \"%s\" has no value named \"%s\".
 mapWithModifier = Field labels (required/optional/repeated) are not allowed on map fields.