Solaris change

[Dave Love]

I've just installed a change that got forgotten about a while back to
enable use of GNU malloc on Solaris 2.5+.  This is likely to break on
some systems, but we'd like to find out more about the circumstances.
(It works OK on Solaris 2.7 here.)

If it causes you grief, uncomment the SYSTEM_MALLOC definition in
src/s/sol2-5.h and please report details of your system.  How it's
patched may be important as well as the basic release number.  If you
can actually figure out what the problem is (there are hints in that
config file), that would be great.