tox configuration enhanced

argparse is now only installed by py26
setenv defined for testlink demo application as default
py.test results are now logged as junit xml
unittest configuration enhanced

tox and travis installs unittest2 now only for py26
tox config extend to run examples

[skip ci]
utest-offline test__getAttachmentArgs_textfile added to reporduce #39

test passed under py27 and fails under py34