Add Adobe a.out support.

Add Adobe a.out support.

* aout-adobe.c:  New file.  So far, only reads a.out.adobe.  FIXME.
* config/adobe.mt:  Add.
* configure.in (*-adobe-* target):  Add.
* targets.c (a_out_adobe_vec):  Add.
* Makefile.in:  add aout-adobe.c.

* configure.in:  Put two dashes in all entries to be matched.
Add comments to remind people to do this.
Reorder all entries that match manufacturer names, to occur
last, so they will only be matched if no more specific match
occurs.  Remove manufacturers `aout', `bout', `coff', and `elf'.