Sitecustomize files can be slow or broken and might hang editor
startup. Since they aren't necessary for checking the python version,
disable them to get a small speed boost for everyone, and an editor
that doesn't hang indefinitely on startup if the sitecustomize gets
into an infinite loop (due to a bad NFS mount or similar).
Display an error message to the user depending on the status code
returned by the ycmd server.
Remove ycm_core checks in plugin/youcompleteme.vim. These checks are
now done by the ycmd server.
Do not start a separate process to check the core version but rely on
ycmd returning a specific exit code. This slightly improves the Vim
startup time.
Rename CheckPythonVersion to IsPythonVersionCorrect.
In embedders, sys.executable may contain a Vim path instead of a Python
one. To avoid starting a Vim instance in this case, we check that given
path ends with a Python 2.6 or 2.7 name using a regex.
Add tests for this regex.
