Fix false warning for smarttabs and indentation within multiline comment blocks

When indenting with tabs, lines within comment blocks are prefixed with a space (for alignment) and an asterisk, followed by another space.  Pretty standard pattern.

This causes a false alarm when indenting within comment blocks (e.g. for a code sample in a Markdown-flavored doc engine).

### Example:

    /**
    .*.Usage:
    .*
    .*.---->do.something();
    .*/

Throws:

> Mixed spaces and tabs.

### Notes:

The patch is a little hacky to look for `*` since it's in a comment block and syntactically meaningless, but at a glance it looks like [line 1322](https://github.com/jshint/jshint/blob/master/src/stable/lex.js#L1322) (right below my patch) is doing the same thing.

This might be irrelevant with changes to -next, especially if that has a better concept of multiline statements, but [package.json](https://github.com/jshint/jshint/blob/master/package.json#L18) is still referring to -stable.

### Related issues:

#644