Add section table to objfile struct. Use it for find_pc_section.

Add section table to objfile struct.  Use it for find_pc_section.
* objfiles.c (add_to_objfile_sections,
  build_objfile_section_table, find_pc_section): new functions.
  (allocate_objfile): build section table.
* objfiles.h (struct obj_section): new structure.
  (struct objfile): add section table.
  (find_pc_section): new prototype.
* solib.[ch] (find_pc_section_from_so_list): removed.
* sparc-tdep.c: include objfiles.h for find_pc_section.  include
  symfile.h for objfiles.h.
  (in_solib_trampoline): adjusted for new find_pc_section
  prototype.  Removed BAD_RICH_HACK ifdefs.
* symfile.c (syms_from_objfile): offset objfile sections.
  (find_pc_section): removed.  Also removed BAD_RICH_HACK ifdefs.
* symfile.h (find_pc_section): prototype removed.  Also fixed
  comment typo NUL -> NULL.
* target.[ch] (find_pc_section_from_targets): removed.
* config/sparc/tm-sun4sol2.h (BAD_RICHH_HACK): removed.