Fix two warnings

One about read's result not being used,
second one about an unused doc comment.
This commit does a breaking API change.

src/context/mod.rs

@@ -517,19 +517,17 @@ impl Context {
     /// let pixels: Vec<Vec<(u8, u8, u8, u8)>> = display.read_front_buffer();
     /// # }
     /// ```
-    pub fn read_front_buffer<T>(&self) -> T
+    pub fn read_front_buffer<T>(&self) -> Result<T, ops::ReadError>
                                 where T: texture::Texture2dDataSink<(u8, u8, u8, u8)>
     {
         let mut ctxt = self.make_current();
         let dimensions = self.get_framebuffer_dimensions();
         let rect = ::Rect { left: 0, bottom: 0, width: dimensions.0, height: dimensions.1 };
 
-        // FIXME: See https://github.com/glium/glium/pull/1682#issuecomment-375596152
-        // Leave it unchecked for now, it will generate warning as a reminder it needs fixing.
         let mut data = Vec::with_capacity(0);
         ops::read(&mut ctxt, ops::Source::DefaultFramebuffer(gl::FRONT_LEFT), &rect,
-                          &mut data, false);
-        T::from_raw(Cow::Owned(data), dimensions.0, dimensions.1)
+                          &mut data, false)?;
+        Ok(T::from_raw(Cow::Owned(data), dimensions.0, dimensions.1))
     }
 
     /// Execute an arbitrary closure with the OpenGL context active. Useful if another

src/lib.rs

@@ -117,6 +117,7 @@ pub use program::ProgramCreationError::{CompilationError, LinkingError, ShaderTy
 pub use sync::{LinearSyncFence, SyncFence};
 pub use texture::Texture2d;
 pub use version::{Api, Version, get_supported_glsl_version};
+pub use ops::ReadError;
 
 use std::rc::Rc;
 use std::thread;

src/program/mod.rs

@@ -55,8 +55,8 @@ pub fn is_subroutine_supported<C: ?Sized>(ctxt: &C) -> bool where C: Capabilitie
     ctxt.get_version() >= &Version(Api::Gl, 4, 0) || ctxt.get_extensions().gl_arb_shader_subroutine
 }
 
-/// Some shader compilers have race-condition issues, so we lock this mutex
-/// in the GL thread every time we compile a shader or link a program.
+// Some shader compilers have race-condition issues, so we lock this mutex
+// in the GL thread every time we compile a shader or link a program.
 // TODO: replace by a StaticMutex
 lazy_static! {
     static ref COMPILER_GLOBAL_LOCK: Mutex<()> = Mutex::new(());