Don't stat each directory as it's being added to the path in
%enumerate-directories. 

This makes this part of the function the same as the version from
18a.  Don't see any real reason why stat was required anyway.
Don't need to compile undefineds.c on sparc.
Fix error in computation (log number base) where one of the args is a
double-double.

 * src/code/irrat.lisp:
   * For the following two cases, cmucl generated an error instead of
     computing the log
     * Base is a double-double but number is not.
     * Number is a double-double but base is not.
 * tests/irrat.lisp:
   * Add some tests for log2 and log10.