Cleaned the FeatureContext a bit

Running Behat in a different folder should not involve changing the
current directory of the main behat process.
Forced the paths.base to use a real path all the time

It looks like PHP on Windows sometimes decide to report the path to the
working directory using the old DOS paths shortening the folder names
instead of using the real path, making string replacements of the base
path fail.
Merge pull request #431 from stof/clean_testsuite

Clean the FeatureContext a bit