Make indexing_slicing a restriction lint (fixes #2933)

Author: Manishearth

clippy_lints/src/indexing_slicing.rs

@@ -80,7 +80,7 @@ declare_clippy_lint! {
 /// ```
 declare_clippy_lint! {
     pub INDEXING_SLICING,
-    pedantic,
+    restriction,
     "indexing/slicing usage"
 }
 

clippy_lints/src/lib.rs

@@ -407,6 +407,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>) {
         arithmetic::INTEGER_ARITHMETIC,
         assign_ops::ASSIGN_OPS,
         else_if_without_else::ELSE_IF_WITHOUT_ELSE,
+        indexing_slicing::INDEXING_SLICING,
         inherent_impl::MULTIPLE_INHERENT_IMPL,
         literal_representation::DECIMAL_LITERAL_REPRESENTATION,
         mem_forget::MEM_FORGET,
@@ -437,7 +438,6 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>) {
         enum_variants::PUB_ENUM_VARIANT_NAMES,
         enum_variants::STUTTER,
         if_not_else::IF_NOT_ELSE,
-        indexing_slicing::INDEXING_SLICING,
         infinite_iter::MAYBE_INFINITE_ITER,
         items_after_statements::ITEMS_AFTER_STATEMENTS,
         matches::SINGLE_MATCH_ELSE,