Now we're using conditions to signal file-handling errors too.
The code handling sequences was reorganized.
1. DNA-STRING type definition was moved to the GAS-DNA package (with
   the comparison function, DNA-STRING-EQUAL).
2. A class GAS-DNA:SEQUENCE was added to store data about sequences
   being processed.
3. Package interfaces were updated.
FASTA and ABIF parsers now return GAS-DNA:SEQUENCE objects.
We pass the name of the sequence to the CLOSE command without checking
it with PROBE-FILE.
I made a foolish mistake, but to err is human, isn't it?  I've also
renamed the variable *FILE-TYPE-ALIST* to *SUPPORTED-TYPES-ALIST*.
Two important changes:
1. workspace hash-tables now use EQUAL test-function;
2. new sequence-file handling code from GAS-DNA was incorporated into
   this package.
Sometimes FASTA files come with a "seq" extension.
Little changes in "ls" and "lw" commands:
- both commands use ~A directive to display data,
- "ls" command does nothing if there is no current workspace.
More small changes:
- CURRENT-WORKSPACE and CURRENT-WORKSPACE-NAME displays a message on
  *ERROR-OUTPUT* instead of signaling an error condition with ERROR;
- LIST-SEQUENCES handles the case of no current workspace instead of
  relying on the workspace to be set.
Added license information.
Added a DEFCONSTANT macro (shadowing the one from the CL package) to
the GAS-UTILS package.  License information was also added.