message: fix error message details
diff: use std::convert::TryFrom;
  -use rustc::ty::{Ty, layout::{Size, Align, LayoutOf}};
  +use rustc::ty::{Ty, layout::{Size, LayoutOf}};
  use rustc::mir;
  use crate::*;
  @@ -110,14 +110,15 @@ impl<'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'mir, 'tcx> {
  let offset = offset
  .checked_mul(pointee_size)
  .ok_or_else(|| err_panic!(Overflow(mir::BinOp::Mul)))?;
  - // We do this forst, to rule out overflows.
  + // We do this first, to rule out overflows.
  let offset_ptr = ptr.ptr_signed_offset(offset, self)?;
  // What we need to check is that starting at `ptr`,
  // we could do an access of size `offset`. Alignment does not matter.
  - self.memory.check_ptr_access(
  + self.memory.check_ptr_access_align(
  ptr,
  Size::from_bytes(u64::try_from(offset).unwrap()),
  - Align::from_bytes(1).unwrap(),
  + None,
  + CheckInAllocMsg::InboundsTest,
  )?;
  // That's it!
  Ok(offset_ptr)
  