Fix for Undefined index: _regular_price, _sale_price, _tax_status, _tax_class, _visibility, _purchase_note

Undefined index appears for: _regular_price, _sale_price, _tax_status,
_tax_class, _visibility, _purchase_note, when fields are empty, for
example.

Notice: Undefined index: _tax_class in
woocommerce\admin\post-types\writepanels\writepanel-product_data.php on
line 678
Readme bump for #3159

Conflicts:
	readme.txt
Replaced placeholder plugin

As committed on master branch:
- https://github.com/woothemes/woocommerce/commit/d1fbc3b7f10793848951b3e6ce61662df7cafda6

Conflicts:
	assets/js/frontend/woocommerce.min.js
Check product exists before showing it as an option

As committed on master branch:
- https://github.com/woothemes/woocommerce/commit/28933f1fec2cb2feee2cf43f6d319990f5753088

Conflicts:
	admin/post-types/writepanels/writepanel-product_data.php
2.0.11 version bump

Conflicts:
	readme.txt
	woocommerce.php
Fixed minification for woocommerce.js file
Date bump for 2.0.11
Merge branch 'refs/heads/release-11-fix'

Conflicts:
	assets/js/frontend/woocommerce.min.js
	includes/class-wc-checkout.php
	readme.txt
	woocommerce.php
Rounding tweaks
Put back params
Merge pull request #3326 from justinstern/master

Bugfix: Always Submit Selected Shipping Method on Update Checkout
Change is_visible for variations to make method calls cleaner.
Remove need for pre-ambles - standardize hooks. Closes #3181.
Checkout js
No add to cart redirect, and use POST for add-to-cart Closes #3200
kill helper closes #3332
New dummy data #3119
Enforce session as array data, and settings api tweak for special chars. Closes #3135.
Fixed my merge gone bad
Readme for cross sells merge fix