Stay Python 2.6 compatible

[Elias481]

As there are many installations with only default 2.6 Python in place an no "supported" updates are available in official repos for OS we should try to stay Python 2.6 compatible... (At least all the Redhat/Centos 6 systems are affected.)

Up to now there is "nothing" in PyInotify that is not working with 2.6 and it would be fine if that could last for a while, at least as long enterprise operating systems like Centos/Redhat 6 are supported and offer no official update to Python 2.7. I know there are Python 3.4 packages available for these two via epel, but unfortunately in some companies are still policies in place that enforce pyhton 2.6 for commonly used scripts... And there are companies still having unsupported Centos/Redhat 5 systems in production where the latest version available via epel is 2.6.

• Update .travis.yml include v2.6 and for that version do the following addtional tasks:
• explicitly install pycparser version 2.18 needed by coverall as this is latest version that's 2.6 compatible
• install unittest2 to have the newer unittest features available for 2.6 so only minimal change required for test_inotify.py
• Update test_inotify.py import unittest2 as unittest for python version 2.6
• Update adapters.py change debug code to format syntax understood by 2.6

Drawback of this: the travis test for 2.6 takes quite much time because some dependencies need to be compiled. But I think this is not a big issue.

[coveralls]

Coverage remained the same at 85.069% when pulling 7da545d1af057add68e3c08f18cb91ebaada8c09 on Elias481:try-to-stay_2.6_compatible into 288a2b01fd4a726dc68d960f8351630aee788a13 on dsoprea:master.

[dsoprea]

Let's see if 2.6 is still available in CI. If so, then I'm good with it.