Rename issue-\d+.rs tests to have meaningful names

tests/rustdoc/primitive-raw-pointer-link-15318.rs

@@ -0,0 +1,12 @@
+// aux-build:issue-15318.rs
+// ignore-cross-compile
+
+#![crate_name="issue_15318"]
+#![no_std]
+
+extern crate issue_15318;
+
+// @has issue_15318/fn.bar.html \
+//      '//*[@href="http://example.com/issue_15318/primitive.pointer.html"]' \
+//      '*mut T'
+pub fn bar<T>(ptr: *mut T) {}