Specify path of weighted_matching.dat via Jamfile

[jorisvr]

Test weighted_matching_test.cpp currently expects its input file weighted_matching.dat in the current working directory. As a result, testing fails when invoked via b2 from another working directory.

In previous releases, weighted_matching_test.cpp would silently skip all tests when it failed to open its input file. I "fixed" this in commit f98edae , thus causing the issue.

This commit fixes the issue by specifying the path of weighted_matching.dat via the Jamfile.

Fixes: #426