xscheme bug

[John Lewis <sunybcs!sbcs!nyit!zilla@bingvaxu.cc.binghamton.edu>]

there is a bug in xscheme0.17's (restore) function.  the bug is that garbage
collection should be inhibited during the main part of xlirestore().  This
is because the image is restored in node-array order, rather than obarray order.
For example, strings may be restored before the symbols which refer to them,
and a gc before the corresponding symbol is restored will remove the string (set
its type to FREE).  routines called in xlirestore (e.g. getvspace()) can
trigger gc.
  A fix is simply to set a flag inhibiting gc during the main part of 
xlirestore.  dbetz confirmed that this is a reasonable fix.