Essentially non-functional tidyings and improvements to debuginfo

Essentially non-functional tidyings and improvements to debuginfo
reading.  Two sets of changes:

* New flags for debugging the readers.
  --debug-dump=syms
  --debug-dump=line
  --debug-dump=frames

  These (currently accepted but nonfunctional) are intended to
  create output in the style of (that is, identical to)
    /usr/bin/readelf --syms
    /usr/bin/readelf --debug-dump=line
    /usr/bin/readelf --debug-dump=frames
  respectively.  The plan is that flaws in these readers can then
  be easily found by diff-ing the output against that from readelf.

  Also, a new flag --trace-symtab-patt=<object filename pattern>
  which is used to limit all debuginfo-related debug info to the
  set of shared object names matching the given pattern.  This
  facilitates extracting the debuginfo details of one specific
  shared object, which is usually what is required, rather than
  having to wade through megabytes of junk from every object in
  the process.

* Propagate the avma/svma/image address-naming scheme
  (as described at the top of debuginfo.c) through large parts of
  readelf.c and readdwarf.c.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@6588