Adapt to work with GHC 6.12

- Adapted the package to work with GHC 6.12
- Plugins that depend on the old base3 are currently
  not correctly loaded as the plugin loaded misses
  the dependence on syb (leading to unresolved symbols)
- Cleaned up most of the testsuite (there are still
  some outstanding failures, of which only one
  demonstrates a bug in the plugins library as far
  as I can see — see previous bullet point)
- Cleaned out a little cruft (but more could be done)

testsuite/plugs/runplugs/Makefile

@@ -1,4 +1,4 @@
-GHCFLAGS=   -Onot $(GHC_EXTRA_OPTS)
+GHCFLAGS=   -O0 $(GHC_EXTRA_OPTS)
 PKGFLAGS=   -package posix
 PKGFLAGS+=  -package plugins