Misc: Try to avoid evaluating conditions after window unmap & others

- Try to avoid evaluating conditions after window unmap/destruction.
  Unfortunately, frequently this doesn't work due to the asynchronous
  nature of X.

- Add _GTK_FRAME_EXTENTS exclusion rules to compton.sample.conf. Thanks
  to memeplex, hexchain, and others for info. (#189)

- Add debugging option --show-all-xerrors, and other debugging changes.
  Doc update.
Bug fix #190: Copy shadow/fade state from last paint on unmapped wins

Copy shadow/fade/color-inversion/background-blur state from last paint
on unmapped windows. I hope it doesn't have unexpected side effects.
(#190)
Misc: Fix a possible assert() failure
Bug fix #191: Add rounded-corners detection to --unredir-if-possible

Add `bounding_shape` and `rounded_corners` as condition match target.
Deprecate --shadow-ignore-shaped. Add rounded-corners detection to
win_is_fullscreen(). Slightly modify win_rounded_corners() logic. Thanks
to tdryer for reporting. (#191)