crucible: add cleanup class

Store a function (or closure) in an instance and invoke the function
from the destructor.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

lib/Makefile

@@ -1,8 +1,9 @@
 default: libcrucible.so
 
 OBJS = \
-	crc64.o \
 	chatter.o \
+	cleanup.o \
+	crc64.o \
 	error.o \
 	extentwalker.o \
 	fd.o \

lib/cleanup.cc

@@ -0,0 +1,17 @@
+#include <crucible/cleanup.h>
+
+namespace crucible {
+
+	Cleanup::Cleanup(function<void()> func) :
+		m_cleaner(func)
+	{
+	}
+
+	Cleanup::~Cleanup()
+	{
+		if (m_cleaner) {
+			m_cleaner();
+		}
+	}
+
+}