Only auto-detect Phpakefile in CWD

[jigarius]

Requirements

Turns out that tools like make don't simply lookup a Makefile in parent directories. Need to investigate why they do so and remove that feature from Phpake if required. Alternatively, a confirmation message can be displayed:

A Phpakefile was not found in the current working directory, but one was found in one of the parent directories. Would you like to use that one instead?

[jigarius]

Done. Remove the auto-lookup of Phpakefile in parent directories.