make: always cd into target directory for rules/actions

make: always cd into target directory for rules/actions

Rather than testing for a subdirectory, just always cd into the
appropriate directory.  Even when self.path is empty, we may have
(via --generator-output) the output directory in an unexpected place.
Sourceify() always expands to the proper place, even for '.'.

Committed: http://code.google.com/p/gyp/source/detail?r=998

[Nico, 2011-08-15 21:50:02]

Can you add "Because Sourceify('') != '' if --generator-output is set" to the CL
description? A TEST= line might help future archeologists help understand the
motivation behind this change, too.

LGTM