Misleading 'unknown type' error when tabs are used.

[utting]

When tabs are used at the beginning of a line in a Whiley file, the error message says 'unknown type encountered' on the following keyword or type. This is misleading - it would be helpful if it gave an error that said tabs are not allowed. For example, the attached test2.whiley file gives the error: $ wy build .\src\test2.whiley:4: unknown type encountered return x ^^^^^^

test2.whiley.txt