Merge revisions 14255, 14293, and 14294 from the BUF_REMOVAL branch to trunk.

Merge revisions 14255, 14293, and 14294 from the BUF_REMOVAL branch to trunk.
The functions VG_(get_filename) and VG_(get_filename_lineno) now return
a pointer to filename and directory name instead of copying them into
buffers passed in from the caller.
The returned strings are persistent as long as the DebugInfo to which
they belong is not discarded. The caller therefore needs to stash them
away as needed.
Function VG_(strncpy_safely) has been removed as it is no longer needed.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14668