Fix a problem on i386 systems where buffered code stream access was failing

Fix a problem on i386 systems where buffered code stream access was failing
to take into account the minimum size granularity of the code section.  For
now, the buffering is simply disabled until it can be done right.
There is still a similar problem in the i386 disassembly code for locations
within 20 bytes of the end of the code segment.