selectors2: do not use platform.system() `platform.system()` may have a side effect spawning a shell executing `uname -p`, which may print a warning when the current directory is removed: shell-init: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory This patch changes selectors2 to test the `sys.platform` string, which is a much safer way to detect Jython. Jython's `sys.platform` looks like this: Jython 2.7.1 (default:0df7adb1b397, Jun 30 2017, 19:02:43) [OpenJDK 64-Bit Server VM (Oracle Corporation)] on java1.8.0_144 Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> sys.platform 'java1.8.0_144 ( ==linux2 for targets )' Differential Revision: https://phab.mercurial-scm.org/D1018