improve non_upper_case_globals diagnostics

Use a structured suggestion and tighten the span to just the identifier.

src/test/ui/lint/lint-lowercase-static-const-pattern.rs

@@ -0,0 +1,51 @@
+// Issue #7526: lowercase static constants in patterns look like bindings
+
+#![allow(dead_code)]
+#![deny(non_upper_case_globals)]
+
+#[allow(non_upper_case_globals)]
+pub const a : isize = 97;
+
+fn f() {
+    let r = match (0,0) {
+        (0, a) => 0,
+        //~^ ERROR constant in pattern `a` should have an upper case name
+        (x, y) => 1 + x + y,
+    };
+    assert_eq!(r, 1);
+}
+
+mod m {
+    #[allow(non_upper_case_globals)]
+    pub const aha : isize = 7;
+}
+
+fn g() {
+    use self::m::aha;
+    let r = match (0,0) {
+        (0, aha) => 0,
+        //~^ ERROR constant in pattern `aha` should have an upper case name
+        (x, y)   => 1 + x + y,
+    };
+    assert_eq!(r, 1);
+}
+
+mod n {
+    pub const OKAY : isize = 8;
+}
+
+fn h() {
+    use self::n::OKAY as not_okay;
+    let r = match (0,0) {
+        (0, not_okay) => 0,
+//~^ ERROR constant in pattern `not_okay` should have an upper case name
+        (x, y)   => 1 + x + y,
+    };
+    assert_eq!(r, 1);
+}
+
+fn main () {
+    f();
+    g();
+    h();
+}