Asyncpg sensitive to build info in version number #261

• asyncpg version:
  0.14.0

• PostgreSQL version:
  Many pg10 versions with extra build/variant version info. For example, the current docker latest image for 10.2: https://github.com/docker-library/postgres/blob/674466e0d47517f4e05ec2025ae996e71b26cae9/10/Dockerfile

• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?:
  This is easily reproducible with a local PostgreSQL install, either using the docker image linked above or by installing the standard repository version from ubuntu 18.04 (reproduced with 10.2-1 from repository http://us.archive.ubuntu.com/ubuntu bionic/main amd64).

• Python version:
  3.6.4

• Platform:
  intel amd64 ubuntu 18.04 in vmware, linode amd64 ubuntu 16.04

• Do you use pgbouncer?:
  No

• Did you install asyncpg with pip?:
  Yes

• If you built asyncpg locally, which version of Cython did you use?:
  n/a

• Can the issue be reproduced under both asyncio and
  uvloop?:
  Yes

Whenever a connection is established to the server, the server version string goes through overly stringent parsing that will break if anything remotely unexpected appears in the version string. Several new versions of postgres server I have encountered include build information in parentheses after the numeric version. For example, a real value encountered: '10.2 (Ubuntu 10.2-1)'.

This will cause errors like the following:

ValueError: invalid literal for int() with base 10: '2 (Ubuntu 10'

ValueError: invalid literal for int() with base 10: '2 (Debian 10'

...at line serverversion.py:46, versions = [int(p) for p in parts][:3], in split_server_version_string().

Tiptoeing around this strange restriction by installing from very specific repositories and build versions is becoming cumbersome in CI configuration and deployment, where a minor upgrade to a newer, stable-channel version of postgres server completely breaks Asyncpg's ability to connect to it.