Ensime recipe uses `dist/elisp' directory for load-path.

Related to #892.

I had a couple of ideas how to fix ensime recipe:
- I tried `:load-path ,(progn ...)`; turns out el-get expects stringp
- I tried `(el-get-add-path-to-list 'ensime 'load-path (car (directory-files ...)))` in :post-init; turns-out that is a little to late because `(require 'ensime)` precedes :load-path
- and a couple of others; learning something about el-get internals along the way :)

In the end, this implementation is the most straightforward even though it is OS dependent.

Anyway, hope that helps.