Misc: --write-pid-path & small changes

- Add --write-pid-path to write process ID to a file, to help
  determining compton's process ID when -b is used.

- Add a few extra targets to query through D-Bus opts_get (version, pid,
  etc.) and through win_get, primarily for debugging.

- Add helper macros likely(), unlikely(), cmalloc(), ccalloc(),
  crealloc().

- Change w->opacity_set to opacity_t. Determine display_repr in
  session_init(), etc.
Misc: Add properties to the registration window

Add WM_CLASS, COMPTON_VERSION, and _NET_WM_PID properties to the
registration window, to ease the development of pcman's compton-conf.
Feature: Add XRender-GLX hybird backend

- Add new backend "xr_glx_hybird", which uses X Render for all
  compositing but GLX on the last step of rendering to screen.  This
  makes GLX-backend-specific VSync methods usable while may avoid
  certain bugs with GLX backend. The idea comes from ali1234.
  Experimental.

- GLX backend: Stop using or rendering to depth buffer.

- Use glFinish() instead of glFlush() before VSync. It probably uses
  more CPU but could be more reliable than glFlush().
Misc #152: Fix a spelling mistake

Fix a spelling mistake (xr_glx_hybird -> xr_glx_hybrid). Thanks to cju
for reporting.
Misc #163: Make usage of glFinish() optional

Make usage of glFinish() optional to avoid high CPU usage. (#163)
Fix typo: s/hybird/hybrid/
Window Color Inverter

Assign to a hotkey: toggle (focused) window color inversion.

Good accessibility enhancement.

Obviously, stripped right out of the examples.
Merge branch 'richardgv-dev'
Window Color Inverter

Added richardgv's improvements
+Invert mouse-selected window (+default behavior)
+Invert window with specified window-id
+Help output (minimal catchall)

inverter.sh [ selected | focused | window-id ]
Window Color Inverter
+Improved help output for bad window-id
Window Color Inverter
+lastfix: forgot to grep -w for window-id to avoid false-positves
Window Color Converter
+reallylastfix: One more comment; that's all.
Merge pull request #164 from quequotion/patch-1

Window Color Inverter
Misc: Adjust inverter.sh slightly

- inverter.sh: Fix the incorrect rejection of hexadecimal window IDs.

- inverter.sh: Use "invert_color" instead of "invert_color_force" to
  determine target window inversion status.
Merge branch 'master' of git://github.com/chjj/compton into develop