Merge r14288 from the BUF_REMOVAL branch to trunk.

Merge r14288 from the BUF_REMOVAL branch to trunk.
What it does it changing cachegrind's get_debug_info function such
that it no longer builds up an absolute pathname. Instead the function
get an additional parameter for the directory name and the absolute
pathname is built when it is needed. This will come in handy soonish
when VG_(get_filename_lineno) will be changed and those buffers will
disappear.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14665