configure: Make cheese detection auto

Simply detect cheese availability, and build with if it is.
This helps people jhbuilding the gnome-shell moduleset.

configure.ac

@@ -160,11 +160,14 @@ AM_CONDITIONAL(BUILD_PRINTERS, [test x"$enable_cups" = x"yes"])
 # Optional dependency for the user accounts panel
 AC_ARG_WITH([cheese],
             AS_HELP_STRING([--with-cheese], [enable cheese webcam support]),,
-            with_cheese=yes)
+            with_cheese=auto)
 
 if test x"$with_cheese" != x"no" ; then
-   PKG_CHECK_MODULES(CHEESE, gstreamer-0.10 cheese-gtk >= 2.29.90)
-   AC_DEFINE(HAVE_CHEESE, 1, [Define to 1 to enable cheese webcam support])
+   PKG_CHECK_MODULES(CHEESE, gstreamer-0.10 cheese-gtk >= 2.29.90, [have_cheese=yes], [have_cheese=no])
+   AM_CONDITIONAL(BUILD_CHEESE, test x${have_cheese} = xyes)
+   if test x${have_cheese} = xyes; then
+     AC_DEFINE(HAVE_CHEESE, 1, [Define to 1 to enable cheese webcam support])
+   fi
 fi
 
 # This is a hard-dependency for the region and user-accounts panels

panels/user-accounts/Makefile.am

@@ -16,9 +16,12 @@ AM_CPPFLAGS =						\
 	-I$(srcdir)/../common/				\
 	$(PANEL_CFLAGS)					\
 	$(USER_ACCOUNTS_PANEL_CFLAGS)			\
-	$(CHEESE_CFLAGS)				\
 	$(DISABLE_DEPRECATED)
 
+if BUILD_CHEESE
+AM_CPPFLAGS += $(CHEESE_CFLAGS)
+endif
+
 MARSHALFILES = marshal.c marshal.h
 BUILT_SOURCES = $(MARSHALFILES)
 
@@ -67,11 +70,14 @@ libuser_accounts_la_SOURCES =		\
 libuser_accounts_la_LIBADD = 		\
 	$(PANEL_LIBS)			\
 	$(USER_ACCOUNTS_PANEL_LIBS)	\
-	$(CHEESE_LIBS)			\
 	$(top_builddir)/panels/common/liblanguage.la \
 	-lcrypt				\
 	-lm
 
+if BUILD_CHEESE
+libuser_accounts_la_LIBADD += $(CHEESE_LIBS)
+endif
+
 libuser_accounts_la_LDFLAGS = $(PANEL_LDFLAGS)
 
 EXTRA_DIST = \