defines for the blocks of a blockvector that contain global and
file-static symbols and the first of the smaller scope contours.
* mipsread.c: Use them.
* coffread.c (end_psymtab): Free named symtabs and psymtabs for
a file, once a new symtab has been read for it.
* mipsread.c: FIXME. We need to do the same for MIPS, but it
looks harder to determine the top-level block before it's been
queued to the psymtab list.