Fix bug that broke signal handlers.

The #if check in C was using the wrong case for an identifier,
resulting in the signal handlers not being installed or used.

This broke the HARP runtime when certain things happened, such
as a divide by zero or an overflow.
Bump to current testworks.
Revert "[rt] We no longer need chain_sigaction."

This reverts commit 0a8df6490915eceeb413a17828388d190b682e7b.

We see crashes in signal handling without chain_sigaction,
so re-instate that code until we can look into it further.
Add links to other useful string functions outside the strings library.
Merge pull request #605 from enlight/master

Add links to other useful string functions outside the strings library.
[doc,strings] Add additional useful methods.
[doc,strings] Clean up formatting a bit.
[docs,streams] Fix formatting.
Fix copy/paste error with jam-includes.

Fixes #526.
Add hash-algorithms library to standard libraries.

sources/lib/hash-algorithms: The code.

Makefile.in: Add tests to 'make check'

documentation/library-reference: Document it.

documentation/release-notes: Add release note.

sources/registry/generic/hash-algorithms*: Add registry entries.
[doc,hash-algorithms] Clarify wording.
[doc,hash-algorithms] Expand on update-hash / digest.
Bump to the new version.
[doc,streams] Use new type directives.
[doc,streams] Missing #key parameters.
[doc,format-out] Document new force-out function.