reStructured Text: initial indents are ignored in line blocks (starting with "|") (BB-14659)

In this example:

| Roses are read
|     violets are blue

the second line should appear indented in the output. It is how rst2html renders it (at least in Docutils 0.11, haven't checked other versions) and the reST specification explicitly says, “Initial indents are also significant, resulting in a nested structure.” But BitBucket ignores initial indents and displays the second line without any indentation.