Confusing use of single quote char in error messages

Error messages involving the `'` single quote character can be hard to read.

**Repro steps**

1. Evoke a compiler error in which quoted material is intermixed with `'` used for types `'a` and values `x'`.

**Expected behavior**

Appropriate use of characters: `‘` for open quote, `’` for close quote, and `'` for program text
`Type mismatch. Expecting a     ‘(string * string) array -> 'a’ but given a     ‘(string * string) array -> seq’ The type ‘int list -> 'a’ does not match the type ‘string’`

**Actual behavior**

The ASCII single quote character `'` is used in all three situations.
`Type mismatch. Expecting a     '(string * string) array -> 'a' but given a     '(string * string) array -> seq' The type 'int list -> 'a' does not match the type 'string'`

**Known workarounds**

none

**Related information**

Some fonts are not so good at differentiating these three glyphs. Those fonts will eventually be improved or fall out of use, so this simple fix should not be passed over for lack of 100% good fonts.