Use old 1.51 toolchain instead of bleeding edge (#505)

* Use old 1.51 toolchain instead of bleeding edge

1.52 and 1.53 has problems with incremental compilation,
so some people chose to stay on 1.51 for now.

So let's make sure egui supports 1.51 for a while!

* Update to cint 0.2.2 to get rust 1.51.0 compatability

epaint/Cargo.toml

@@ -26,7 +26,7 @@ emath = { version = "0.12.0", path = "../emath" }
 
 ahash = { version = "0.7", features = ["std"], default-features = false }
 atomic_refcell = { version = "0.1", optional = true } # Used instead of parking_lot when you are always using epaint in a single thread. About as fast as parking_lot. Panics on multi-threaded use.
-cint = { version = "^0.2.1", optional = true }
+cint = { version = "^0.2.2", optional = true }
 ordered-float = { version = "2", default-features = false }
 parking_lot = { version = "0.11", optional = true } # Using parking_lot over std::sync::Mutex gives 50% speedups in some real-world scenarios.
 rusttype = "0.9"

epaint/src/lib.rs

@@ -1,12 +1,14 @@
 //! 2D graphics/rendering. Fonts, textures, color, geometry, tessellation etc.
 
-#![cfg_attr(not(debug_assertions), deny(warnings))] // Forbid warnings in release builds
-#![deny(
-    rustdoc::broken_intra_doc_links,
-    rustdoc::invalid_codeblock_attributes,
-    rustdoc::missing_crate_level_docs,
-    rustdoc::private_intra_doc_links
-)]
+// Forbid warnings in release builds:
+#![cfg_attr(not(debug_assertions), deny(warnings))]
+// Disabled so we can support rust 1.51:
+// #![deny(
+//     rustdoc::broken_intra_doc_links,
+//     rustdoc::invalid_codeblock_attributes,
+//     rustdoc::missing_crate_level_docs,
+//     rustdoc::private_intra_doc_links
+// )]
 #![forbid(unsafe_code)]
 #![warn(
     clippy::all,

epaint/src/text/galley.rs

@@ -583,8 +583,6 @@ impl Galley {
 
 #[test]
 fn test_text_layout() {
-    #![allow(clippy::bool_assert_comparison)]
-
     impl PartialEq for Cursor {
         fn eq(&self, other: &Cursor) -> bool {
             (self.ccursor, self.rcursor, self.pcursor)