process_jam_log can't open output file when using library_test_all.sh

[Niklas Angare <li51ckf02@…>]

When I run tools/regression/src/library_test_all.sh on Boost 1.55, it fails to generate proper reports for many libraries. process_jam_log outputs messages like this:

*****Warning - can't open output file: c:/Arbete\boost\boost_1_55_0\../../bin.v2/libs/atomic/test/native_api.test/qcc-arm_4.4.2_0x/debug/link-static/target-os-qnxnto/threading-multi\test_log.xml

The "../../" shouldn't be there as it escapes BOOST_ROOT. The problem seems to be that paths in bjam.log are relative to sub-directories of BOOST_ROOT/libs. The function parse_skipped_msg_aux() appears to handle the case where paths are relative to immediate sub-directories of BOOST_ROOT, such as BOOST_ROOT/status. The attached patch extends it to handle arbitrarily deep sub-directories.