Relative urls in readme.md files only work half the time. (BB-7521)

I have the following project structure:

doc/
    getting_started.md
    ...
readme.md

In my readme.md file, I link to the getting_started.md document like so:

[Get started](doc/getting_started.md)

When viewing the readme.md file in the source tab this link 404's (it points to ../project/doc/contributing.md)

But when I click on the readme.md file and view it, the link works (correctly points to ../project/src/31...8e/doc/contributing.md)

There is a (possibly?) subtly different problem for relative links in sub-folders. Given the project structure of:

doc/
    style/
        markdown.md
    readme.md
top_level_readme.md

In the readme.md file, if I have a link to style/markdown.md as follows:

[Markdown Style Guide](style/markdown.md)

It will break in a similar manner to the above (50% of the time), but with the following urls:

Overview page links to: ../project/src/31...8e/style/markdown.md

While viewing readme.md links to: ../project/src/31...8e/doc/style/markdown.md