* dbxread.c (dbx_symfile_init): Init stab_section_info to NULL to

* dbxread.c (dbx_symfile_init):  Init stab_section_info to NULL to
prevent crashes when examining cross-targets.
* dbxread.c (process_one_symbol):  Include directory name when
calling start_subfile for SOL & BINCL symbols.  This allows gdb to
find include files, and yacc/lex sources when the cwd doesn't match
that in which the object was compiled.
* objfiles.h (ALL_MSYMBOLS):  Don't seg fault when there are no
msymbols.
* symtab.c (lookup_symtab_1):  Rewrite.  It now handles include
files.