Add new lint: non_uppercase_pattern_statics, for #7526.

This tries to warn about code like:
    ```rust
    match (0,0) {
        (0, aha) => { ... },
        ...
    }
    ```
where `aha` is actually a static constant, not a binding.

src/libstd/num/f32.rs

@@ -11,6 +11,7 @@
 //! Operations and constants for `f32`
 #[allow(missing_doc)];
 #[allow(non_uppercase_statics)];
+#[allow(non_uppercase_pattern_statics)];
 
 use default::Default;
 use libc::c_int;

src/libstd/num/f64.rs

@@ -12,6 +12,7 @@
 
 #[allow(missing_doc)];
 #[allow(non_uppercase_statics)];
+#[allow(non_uppercase_pattern_statics)];
 
 use default::Default;
 use libc::c_int;