Expose fork and exec* functions.

[hellozyemlya]

os.py check for existence of this functions, but they are not exposed from posix module. Make them exposed to ensure that os module looks more like default "native" os module.

[jeff5]

Thanks for tying this. Travis shows a failure, but I think it is unconnected with the patch.

However, when it is applied locally, I get this when I try to use execv at the prompt (works in CPython 3):

>>> os.execv("C:\\Windows\\notepad.exe", ["test.tmp"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NotImplementedError: egid

In Linux it seems to work, but my terminal is messed up (no echo).

There are no tests, which may be a matter of merging in from CPython stdlib. (What happens here is that, while a lot of tests come from lib-python, when we need to tweak one, we fork it into our ~/Lib, but then they fossilise.)

[jeff5]

Unfortunately a PR (unlike an issue) cannot be transferred to the new official home at https://github.com/jython/jython. Keeping this open in the frozen-mirror to allow for further consideration.