Add libcap component

This is required in order to compile lxc.

component/libcap/buildout.cfg

+[buildout]
+
+extends =
+  ../attr/buildout.cfg
+
+parts = libcap
+
+[libcap2]
+recipe = slapos.recipe.build
+format = no
+url = http://pkgs.fedoraproject.org/lookaside/pkgs/libcap/libcap-2.22.tar.bz2/ce64058bdb3f086ddbfca8ce6c919845/libcap-2.22.tar.bz2
+md5sum = ce64058bdb3f086ddbfca8ce6c919845
+attr-include = ${attr:location}/include/
+attr-lib = ${attr:location}/lib/
+slapos_promise =
+  directory:sbin
+  directory:usr/include
+  statlib:lib/libcap.a
+  file:lib/libcap.so
+  file:sbin/getcap
+  file:sbin/setcap
+script =
+  import os
+  url = self.download(self.options['url'], self.options['md5sum'])
+  extract_dir = self.extract(url)
+  workdir = guessworkdir(extract_dir)
+  cflags = '-I%(attr)s' % {'attr': self.options['attr-include']}
+  ldflags = '-L%(attr)s -Wl,-rpath=%(attr)s' % {'attr': self.options['attr-lib']}
+  call(['make', 'CFLAGS=%s' % cflags, 'LDFLAGS=%s' % ldflags, 'DESTDIR=%s' % self.options['location'], 'install'],
+       cwd=workdir, env=env)
+  lib64 = os.path.join(self.options['location'], 'lib64')
+  lib = os.path.join(self.options['location'], 'lib')
+  # XXX: Dirty if case
+  #      if lib64 exists, then create a symlink from lib to lib64
+  os.path.exists(lib64) and os.symlink(lib64, lib)
+
+[libcap]
+<= libcap2