Add dependency on `f` to `projectile` recipe

A recent version [1] of `projectile` depends on the `f` package.

[1] https://github.com/bbatsov/projectile/blob/7f483c525987785716e22f0b364eb6be683a0bbc/projectile.el#L41
el-get-sources: deduplicate :pkgname in docstring
Take sha1 of buffer contents, not buffer

This prevents the sha1 function from attempting and then failing to
encode the buffer contents in the wrong encoding.

* methods/el-get-http.el (el-get-http-compute-checksum): Call `sha1' on
  result of `buffer-string', not `current-buffer'.
Add rails-new.
Fix foo-mode-on functions descriptions in :prepare
Add :prepare blocks for some recipes

Add autoloads and/or foo-mode-on functions
 in :prepare block for:

- recipes/ace-jump-mode.rcp
- recipes/auto-indent-mode.rcp
- recipes/pp-c-l.rcp
- recipes/window-number.rcp
- recipes/windsize.rcp
Merge pull request #2003 from Pitometsu/pitometsu

Add :prepare blocks for yet more recipes
Update python.el recipes to point to the GNU Emacs repo
add recipe ac-capf
fix reciple ac-capf
Merge pull request #2007 from stardiviner/recipe_ac-capf

add recipe ac-capf
Add dropbox client.