reStructuredText: link fragments {require, are created with} non-standard prefix='#rst-header-' (BB-12993)

reST does not specify any prefix for link fragments within a document. Accordingly, standard reST rendering tools (like restview) used for local reST rendering (e.g., for pre-commit previewing) generate internal links without a fragment prefix. E.g., the document rst_link_test/README.rst has a first section with name='summary'. When rendering the table of contents for that document, restview creates an internal link like localhost/#summary.

However, Bitbucket's reST renderer creates internal link/anchor fragments prefixed #rst-header- rather than just #. As a result, if a user cut'n'pastes fragments from her/his local renderer into her/his reST source (e.g., creating internal links from one part of her/his documentation to another), the links will resolve/navigate correctly when rendered locally, but will fail when pushed to or rendered by BB.