io: add chown

Unfortunately it's not possible to test the happy path: only superusers
can call chown.
test/io/chown: add test for uid=-1 and gid=-1
io/test/chown: add test for the happy path

Since it supposes it's running under fakeroot, it doesn't check that the
permission gets actually changed, but only that the program doesn't
crash.
test/io/chown: improve test for uid=-1 and gid=-1

Ensuring that the program doesn't crash, and also that it doesn't change
the owners of the file.
Clarify future description.
Merge pull request #366 from sungeunchoi/test

Clarify description for separate compilation futures.
Merge pull request #341 from fsouza/chown

io: add chown

merging on behalf of @fsouza
Ignore a couple files that are generated by new io tests.
Merge pull request #367 from thomasvandoren/update-gitignore-for-io

Ignore a couple files that are generated by new io tests.
Fix io/lydia/mkdir/makeWithMode.chpl on mac.

stat call in the bash script was not supported on mac. Instead of figuring out
how to support multiple versions of stat, convert script to python and use its
os.stat function.
Merge pull request #368 from thomasvandoren/portable-stat-prediff

Fix io/lydia/mkdir/makeWithMode.chpl on mac.

stat call in the bash script was not supported on mac. Instead of figuring out
how to support multiple versions of stat, convert script to python and use its
os.stat function.