fix #921 by passing socket.error on to the caller (where it will be ignored)

(cherry picked from commit d5e9f14344849976da74011f6af266ef5f800f2b)
fix version identifier to comply with PEP 440
change PEP-440 version identifier to one that's actually accepted by pip/setuptools
Implement comment from comment on benoitc/gunicorn#921

We don't want to duplicate handling code for socket.error, but we
also have to close the connection properly to prevent reuse. This
change will close the connection, then reraise socket.error for
handle() thereby sidestepping all code duplication, while still
fixing #921.
Revert "change PEP-440 version identifier to one that's actually accepted by pip/setuptools"

This reverts commit 8929e0dd00cccf0ca1891c008d0b4b327c1b25b2.
Revert "fix version identifier to comply with PEP 440"

This reverts commit 8f142d263912e90a091f12b26691762c67f031bf.
Revert "Revert "fix version identifier to comply with PEP 440""

This reverts commit bdfb7095fa9d9d92b657a66444ee704e3ecf027e.
Revert "Revert "change PEP-440 version identifier to one that's actually accepted by pip/setuptools""

This reverts commit 4004ba6479b37596b3ac6ea2559ece117544a7c0.
Merge branch 'release/19.1.1+laterpay1' into feature/921-ignore-async-handle_request-socket-error

Conflicts:
	gunicorn/workers/async.py
Remove LaterPay local version identifier
Conflicts:
	gunicorn/__init__.py