std(in|out|err) methods can create multiple mutable references to the same object

[toku-sa-n]

uefi-rs/src/table/system.rs

Lines 79 to 93 in a13ddfe

	pub fn stdin(&self) -> &mut text::Input {
	unsafe { &mut *self.table.stdin }
	}
	/// Returns the standard output protocol.
	pub fn stdout(&self) -> &mut text::Output {
	let stdout_ptr = self.table.stdout as *const _ as *mut _;
	unsafe { &mut *stdout_ptr }
	}
	/// Returns the standard error protocol.
	pub fn stderr(&self) -> &mut text::Output {
	let stderr_ptr = self.table.stderr as *const _ as *mut _;
	unsafe { &mut *stderr_ptr }
	}

I tried to change &self to &mut self, but it was difficult to fix the test codes.

uefi-rs/uefi-test-runner/src/proto/mod.rs

Lines 5 to 17 in a13ddfe

	pub fn test(st: &SystemTable<Boot>) {
	info!("Testing various protocols");
	let bt = st.boot_services();
	find_protocol(bt);
	console::test(st);
	debug::test(bt);
	media::test(bt);
	pi::test(bt);
	shim::test(bt);
	}

Here, boot_services() takes an immutable reference to SystemTable while console::test has to take a mutable reference to SystemTable. This causes the conflict of the mutability of references.

[GabrielMajeri]

@toku-sa-n I've opened #240 to attempt to fix this. Does it provide a reasonable solution to prevent multiple mutable references?