o Fix code deleting psymtab entry from objfile's list.

o	Fix code deleting psymtab entry from objfile's list.
	Only worked if the first element in the list was
	being deleted.
o	When MAINLINE (reading main objectfile and need to
	clear out old data), change elfread.c so that the
	psymbol table is emptied once (in elf_symfile_read)
	instead of multiple times in each *_read_psymtab
	function.
o	For elf_symfile_read, load dwarf2 symbols last
	(so that they are searched for first).
o	In mdebug_psymtab_read, delete check to see if
	symbols for current source file already loaded.
	Test doesn't work for .h files.  Above change
	works better