algorithms_avaiable that respectively list the names of hash algorithms
guaranteed to exist in all Python implementations and the names of hash
algorithms available in the current process.

Renames the attribute new in 3.2a0 'algorithms' to 'algorithms_guaranteed'.

unsupported operation is attempted (for example, writing to a file open
only for reading).

Fix reST in NEWS, and remove NEWS.help (all committers should now know reST anyway, and for those who do not, there is Documenting Python.)

- The entry about shutil.copytree is just a revert of r84524 which
looks like an unfinished edition.
- The use of gender-neutral language (s/his/their/) removes the
implicit assumption that programmer == male (change agreed by Antoine).
- Other changes should be uncontroversial fixes.

I haven’t rewrapped under 80 lines to keep the diffs readable; I’ll
rewrap later.