Table of file names with absolute paths.

The table of file names written to the c or cpp file contains absolute
file paths.  This affects, in particular, profiling.  The c method
__pyx_TraceCall takes as one of its arguments a file name, which will be
read from the table of file names.
Table of file names with relative paths.

The previous commit reveals too much information about the system.  With
this change only modules of the processed package are expanded.  The
expanded path reaches no deeper than the package's root.
Merge branch 'profile_abspath' of github.com:martinra/cython into martinra-profile_abspath
Rename var for clarity.