Feature #16: Advanced window matching

- Add advanced window matching system, capable of matching against
  arbitrary window properties as well as a series of internal
  properties, with 4 additional operators (>, <, >=, <=) useful for
  integer targets, and support of logical operators. The old matching
  system is removed, but compatibility with the format is retained.

- As the new matching system is pretty complicated, and I have no past
  experience in writing a parser, it's pretty possible that bugs are
  present. It also has inferior performance, but I hope it doesn't
  matter on modern CPUs.

- It's possible to disable matching system at compile time with NO_C2=1
  now.

- Add ps->o.config_file to track which config file we have actually
  read. Queryable via D-Bus.

- Parse -d in first pass in get_cfg() as c2 needs to query X to get
  atoms during condition parsing.

- Fix a bug in wid_get_prop_adv() that 0 == rformat is not handled
  correctly.

- Fix incompatibility with FreeBSD sed in dbus-examples/cdbus-driver.sh
  .

- Add recipe to generate .clang_complete in Makefile, used by Vim
  clang_complete plugin.

- Add DEBUG_C2 for debugging condition string parsing. DEBUG_WINMATCH is
  still used for match debugging.

- Rename win_on_wdata_change() to win_on_factor_change().

- Extra malloc() failure checks. Add const to matching cache members in
  session_t. Code clean-up. Documentation update.

Makefile

@@ -55,10 +55,10 @@ ifeq "$(NO_DBUS)" ""
 endif
 
 # ==== C2 ====
-# ifeq "$(NO_C2)" ""
-#   CFG += -DCONFIG_C2
-#   OBJS += c2.o
-# endif
+ifeq "$(NO_C2)" ""
+  CFG += -DCONFIG_C2
+  OBJS += c2.o
+endif
 
 # === Version string ===
 COMPTON_VERSION ?= git-$(shell git describe --always --dirty)-$(shell git log -1 --date=short --pretty=format:%cd)
@@ -78,6 +78,9 @@ MANPAGES_HTML = $(addsuffix .html,$(MANPAGES))
 # === Recipes ===
 .DEFAULT_GOAL := compton
 
+.clang_complete: Makefile
+	@(for i in $(filter-out -O% -DNDEBUG, $(CFLAGS) $(INCS)); do echo "$$i"; done) > $@
+
 %.o: src/%.c src/%.h src/common.h
 	$(CC) $(CFLAGS) $(INCS) -c src/$*.c
 
@@ -105,7 +108,7 @@ uninstall:
 	@rm -f "$(DESTDIR)$(MANDIR)/compton-trans.1"
 
 clean:
-	@rm -f $(OBJS) compton $(MANPAGES) $(MANPAGES_HTML)
+	@rm -f $(OBJS) compton $(MANPAGES) $(MANPAGES_HTML) .clang_complete
 
 version:
 	@echo "$(COMPTON_VERSION)"