selectors2: do not use platform.system()...
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
