closes#1814
@kenmcmil: the error messages will now list aliased variables.
For example, in your file, the new error message is:
```
invalid type ascription, term has type
triple (ctxpre c' s_1 ∧ ctxpre c'_1 s_1) (bndngapp b s_1) (ctxpost c' s_1 ∧ ctxpost c'_1 s_1)
but is expected to have type
triple (ctxpre c' s_1 ∧ ctxpre c'_1 s_1) (bndngapp b s_1) (ctxpost c' s_1 ∧ ctxpost c'_1 s_1)
types contain aliased name(s): c'
remark: the tactic `dedup` can be used to rename aliases
state:
...
```
