Harden asInstanceOfOpt to be robust for nulls or reflection crashes.
Reverts logic for unloading units in askLoadedType

The loagic for handling loading/unloading of units in `askLoadedType` was moved
in the compiler side. See https://github.com/scala/scala/pull/3209.  (Also,
mind that this commit should be merged together with the previously linked
scala PR).

This reverts most of the changes made in SHA:
43f8f2bdf4bd99cc85da7f54a0f374be737d4b2f

Re #1001388
Don't create a reconciler for non-editor source configurations.

In the Syntax Coloring preview pane we create a source viewer without an
editor. The reconciler needs an editor to get to the compilation unit, so
we don't attach a reconciler in this case (there won't be any editing).

We might need to revisit this if we ever want to use a source viewer outside
an editor (with reconciliation capabilities).
Merge pull request #594 from dotta/issue/ask-loaded-type

Reverts logic for unloading units in askLoadedType
Merge pull request #596 from dragos/issue/fix-quiescence-syntax-coloring-window-crash

Fix syntax coloring window crash