src: don't error at startup when cwd doesn't exist

The current working directory may not exist when iojs starts up.  Don't
treat that as an error because it's still possible to do many useful
things, like evaluating a command line script or starting a REPL.

This commit also fixes an age-old Windows bug where process.argv[0] was
not properly expanded, that's why the parallel/test-process-argv-0 test
gets an update as well.

Fixes: https://github.com/iojs/io.js/issues/1184
PR-URL: https://github.com/iojs/io.js/pull/1194


Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Rod Vagg <rod@vagg.org>