MAINT-1175 FIX Severe performance issues on 3.3.2 (258114) Release and 3.3.3 (259197) Beta in "Add scroll list item"
removed linear scan for namelist items and used weak reference (LLHandle) instead

We now specialize std::less<const std::type_info*> to use
std::type_info::before(), and on Windows and Mac that Just Works. It even
works on Linux when using gcc 4.4+: more recent implementations of gcc's
std::type_info::before() apparently do name()-string comparisons internally.
It doesn't work so well on Linux with gcc 4.1, though, and that's the compiler
we still use on our Linux build-farm machines. But rather than give up,
perform explicit name()-string comparison in that case.

Instead of forbidding std::map<const std::type_info*, ...> outright (which
includes LLRegistry<const std::type_info*, ...> and LLRegistrySingleton<const
std::type_info*, ...>), try to make it work by specializing std::less<const
std::type_info*> to use std::type_info::before().
Make LLRegistryDefaultComparator<T> use std::less<T> so it can capitalize on
that specialization.

Setting the description column of the linkset floater to be a fixed width.  Having multiple dynamic width columns apparently prevents other columns from being manually resized by the user.

The changeset above touched every consumer of the two LLRegistrySingletons
originally defined with std::type_info* as keys. Those two
LLRegistrySingletons were changed to use const char* as keys, then all
consumers were changed to pass std::type_info::name() instead of the plain
std::type_info* pointer -- to deal with the observed fact that on Linux, a
given type might produce different std::type_info* pointers in different load
modules. Since then, Richard turned up the fascinating fact that at least some
implementations of gcc's std::type_info::before() method already accommodate
this peculiarity. It seems worth backing out the (dismayingly pervasive)
change to see if properly using std::type_info::before() as the map comparator
will work just as well, with conceptually simpler source code.
This backout is transitional: we don't expect things to build/run properly
until we've cherry-picked certain other pertinent changes.