python: update ldconfig(1) cache if sbin/ldconfig exists.

ctypes/util.py::find_library() relies on `ldconfig -p` to load the
appropiate shared libraries required by python modules, and it the cache
is empty it won't be able to load them.

Update the ldconfig(1) but don't update the links.

This fixes the first part of #914.

srcpkgs/python/INSTALL

@@ -0,0 +1,8 @@
+case "${ACTION}" in
+post)
+	# ctypes/util.py find_library() uses ldconfig -p!
+	if [ -x sbin/ldconfig ]; then
+		sbin/ldconfig -X || :
+	fi
+	;;
+esac

srcpkgs/python/template

@@ -4,7 +4,7 @@
 #
 pkgname=python
 version=2.7.9
-revision=3
+revision=4
 wrksrc="Python-${version}"
 hostmakedepends="pkg-config"
 makedepends="