rustc: Rename lints per RFC 344

RFC 344 proposes a set of naming conventions for lints. This commit
renames existing lints to follow the conventions.

Use the following sed script to bring your code up to date:

```
s/unnecessary_typecast/unused_typecasts/g
s/unsigned_negate/unsigned_negation/g
s/type_limits/unused_comparisons/g
s/type_overflow/overflowing_literals/g
s/ctypes/improper_ctypes/g
s/owned_heap_memory/box_pointers/g
s/unused_attribute/unused_attributes/g
s/path_statement/path_statements/g
s/unused_must_use/unused_must_use/g
s/unused_result/unused_results/g
s/non_uppercase_statics/non_upper_case_globals/g
s/unnecessary_parens/unused_parens/g
s/unnecessary_import_braces/unused_import_braces/g
s/unused_unsafe/unused_unsafe/g
s/unsafe_block/unsafe_blocks/g
s/unused_mut/unused_mut/g
s/unnecessary_allocation/unused_allocation/g
s/missing_doc/missing_docs/g
s/unused_imports/unused_imports/g
s/unused_extern_crate/unused_extern_crates/g
s/unnecessary_qualification/unused_qualifications/g
s/unrecognized_lint/unknown_lints/g
s/unused_variable/unused_variables/g
s/dead_assignment/unused_assignments/g
s/unknown_crate_type/unknown_crate_types/g
s/variant_size_difference/variant_size_differences/g
s/transmute_fat_ptr/fat_ptr_transmutes/g
```

Closes #16545
Closes #17932

Due to deprecation, this is a:

[breaking-change]

Author: aturon

src/librustc/driver/driver.rs

@@ -704,15 +704,15 @@ pub fn collect_crate_types(session: &Session,
                 }
                 Some(ref n) if n.equiv(&("bin")) => Some(config::CrateTypeExecutable),
                 Some(_) => {
-                    session.add_lint(lint::builtin::UNKNOWN_CRATE_TYPE,
+                    session.add_lint(lint::builtin::UNKNOWN_CRATE_TYPES,
                                      ast::CRATE_NODE_ID,
                                      a.span,
                                      "invalid `crate_type` \
                                       value".to_string());
                     None
                 }
                 _ => {
-                    session.add_lint(lint::builtin::UNKNOWN_CRATE_TYPE,
+                    session.add_lint(lint::builtin::UNKNOWN_CRATE_TYPES,
                                      ast::CRATE_NODE_ID,
                                      a.span,
                                      "`crate_type` requires a \