Library XBlocks cannot reference assets named "xblock*"

[bradenmacdonald]

1. Upload an image named xblock-something.png to a Text component in a v2 content library.
2. Reference that image in the HTML, as <img src="/static/xblock-something.png" />
3. The image will not display in the preview, due to this code:

edx-platform/common/djangoapps/static_replace/__init__.py

Lines 116 to 119 in 3e43e33

	starts_with_prefix = full_url.startswith(XBLOCK_STATIC_RESOURCE_PREFIX)
	contains_prefix = XBLOCK_STATIC_RESOURCE_PREFIX in full_url
	if starts_with_prefix or (starts_with_static_url and contains_prefix):
	return original

[bradenmacdonald]

I suspect a simple fix for this is only ignoring URLs that start with /static/xblock/ rather than /static/xblock

[ChrisChV]

@jmakowski1123 @lizc577 @sdaitzman @marcotuts This is ready for AC testing on the sandbox