Feature: Issue #29: Alternative shadow blacklist implementation

- Add shadow blacklist feature, but a different implementation from
  nicklan's. 5 matching modes (exact, starts-with, contains, wildcard,
  PCRE) and 3 matching targets (window name, window class instance,
  window general class). Not extensively tested, bugs to be expected.
  It's slower for exact matching than nicklan's as it uses linear search
  instead of hash table. Also, PCRE's JIT optimization may cause issues
  on PaX kernels.

- Add dependency to libpcre. Could be made optional if we have a
  graceful way to handle that in Makefile.

- Some matching functions are GNU extensions of glibc. So this version
  may have troubles running on platforms not using glibc.

- Fix a bug that access freed memory blocks in set_fade_callcack() and
  check_fade_fin(). valgrind found it out.

- Use WM_CLASS to detect client windows instead of WM_STATE. Some client
  windows (like notification windows) have WM_CLASS but not WM_STATE.

- Mark the extents as damaged if shadow state changed in
  determine_shadow().

- Rewrite wid_get_name(). Code clean-up.

- Two debugging options: DEBUG_WINDATA and DEBUG_WINMATCH.

- As the matching system is ready, it should be rather easy to add other
  kinds of blacklists, like fading blacklist.

Makefile

@@ -6,8 +6,10 @@ MANDIR ?= $(PREFIX)/share/man/man1
 
 PACKAGES = x11 xcomposite xfixes xdamage xrender xext
 LIBS = $(shell pkg-config --libs $(PACKAGES)) -lm
+LIBS += $(shell pcre-config --libs)
 INCS = $(shell pkg-config --cflags $(PACKAGES))
-CFLAGS += -Wall
+INCS += $(shell pcre-config --cflags)
+CFLAGS += -Wall -std=c99
 OBJS = compton.o
 
 %.o: src/%.c src/%.h