setup.py now cleanly handles setup-time cython dependency (closes #768)

Customized setup-time dependency installation to work around setuptools'
problematic behavior (closes #798)

Modified lazy dependency scheme to be less hacky (we now subclass
distutils.Distribution).

Removed use of Cython's build_ext (redundant with cythonize):
https://groups.google.com/forum/#!topic/cython-users/fBWLUSJWod0

package/CHANGELOG

@@ -13,7 +13,8 @@ The rules for this file:
   * release numbers follow "Semantic Versioning" http://semver.org
 
 ------------------------------------------------------------------------------
-??/??/16 jandom, abhinavgupta94, orbeckst, kain88-de, hainm, jdetle, jbarnoud
+??/??/16 jandom, abhinavgupta94, orbeckst, kain88-de, hainm, jdetle, jbarnoud,
+         manuel.nuno.melo
 
   * 0.15.0
 
@@ -35,6 +36,8 @@ Enhancements
 
 Fixes
 
+  * setup.py now cleanly handles setup-time Cython dependency (Issue #768)
+    and installs numpy/Cython dependencies system-wide (Issue #798)
   * change_release now finds number and dev (Issue #776) 
   * test_shear_from_matrix doesn't fail for MKL builds anymore (Issue #757)
   * HEADER and TITLE now appear just once in the PDB. (Issue #741) (PR #761)