pycrypto: Add recipe to have support on python3

The pycrypto module sources can be used for both python2 and python3,
but a recipe for python3 was missing, so add it.

Additionally, since the sources (and thus the patches) are shared
between both versions, move the SRC_URI (same on both recipes) to the
common 'python-pycrypto.inc' file, to avoid duplication.

Also, to use the same patch files for both python2 and python3 without
having to duplicate them over 2 folders, change 'python-pycrypto.inc' so
that FILESEXTRAPATHS is prepended with the 'python-pycrypto' local dir
for both versions instead of having that dir named after the package
name '${PN}'.

The python3 recipe is basically the same as for python2, but using
distutils3 instead.

Signed-off-by: Ricardo Silva <rjpdasilva@gmail.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>

meta-python/recipes-devtools/python/python3-pycrypto_2.6.1.bb

@@ -0,0 +1,9 @@
+inherit distutils3
+require python-pycrypto.inc
+
+# We explicitly call distutils_do_install, since we want it to run, but
+# *don't* want the autotools install to run, since this package doesn't
+# provide a "make install" target.
+do_install() {
+       distutils3_do_install
+}