Basic implementation of Copy-On-Write

[alejandroliu]

Implements Copy-On-Write semantics as an Extension to PRoot. It is supposed to be similar to
cowdancer which doesn't work inside
a proot jail.

This is a naive implementation, intended to get a working version quickly.

[vincenthage]

Hi Alejandro,
Great job!

Would you mind adding a test that uses your extension so that it can be fully tested?

[alejandroliu]

I wouldn't mind, but I don't know how the test framework from PRoot works. I see files in the test directory, and I only see a bunch of files with test-XXXXX (which looks quite random to me).

If you can point me to an specific example on how to plug in my test, I would be happy to write one.

[coveralls]

Changes Unknown when pulling 5342c87 on TortugaLabs:cow into ** on proot-me:master**.

[vincenthage]

The travis logs give some commands to execute the tests:
https://travis-ci.org/proot-me/PRoot/jobs/244300611
https://travis-ci.org/proot-me/PRoot/builds/243781511
and it shows that there is an issue the tests on the PR btw:
/home/travis/.travis/job_stages: line 54: [: !=: unary operator expected

I'm also in the process of trying to understand how the tests are done;
from what I see, the tests are listed in the GNUmakefile,

[vincenthage]

As an example,
you can check out @guillon 's test which also involves a new option:
https://github.com/proot-me/PRoot/pull/97/files#diff-968b794e2f95eb8152dcce887f40d455