Various Ethereum related recipes fixes

 * pycryptodome
 * secp256k1
 * pbkdf2

Author: AndreMiras

pythonforandroid/recipes/pbkdf2/__init__.py

@@ -0,0 +1,12 @@
+from pythonforandroid.recipe import PythonRecipe
+
+
+class Pbkdf2Recipe(PythonRecipe):
+
+    # TODO: version
+    url = 'https://github.com/dlitz/python-pbkdf2/archive/master.zip'
+
+    depends = ['setuptools']
+
+
+recipe = Pbkdf2Recipe()

pythonforandroid/recipes/pycryptodome/__init__.py

@@ -5,7 +5,7 @@ class PycryptodomeRecipe(PythonRecipe):
     version = 'v3.4.6'
     url = 'https://github.com/Legrandin/pycryptodome/archive/{version}.tar.gz'
 
-    depends = ['python2', 'setuptools']
+    depends = ['python2', 'setuptools', 'cffi']
 
 
 recipe = PycryptodomeRecipe()

pythonforandroid/recipes/secp256k1/__init__.py

@@ -1,18 +1,20 @@
 from os.path import join
-from pythonforandroid.recipe import CompiledComponentsPythonRecipe
+from pythonforandroid.recipe import PythonRecipe
 
 
-class Secp256k1Recipe(CompiledComponentsPythonRecipe):
+class Secp256k1Recipe(PythonRecipe):
 
     url = 'https://github.com/ludbb/secp256k1-py/archive/master.zip'
 
     call_hostpython_via_targetpython = False
 
     depends = [
         'openssl', 'hostpython2', 'python2', 'setuptools',
-        'libffi', 'cffi', 'libsecp256k1']
+        'libffi', 'cffi', 'libffi', 'libsecp256k1']
 
-    patches = ["cross_compile.patch", "pkg-config.patch", "find_lib.patch"]
+    patches = [
+        "cross_compile.patch", "drop_setup_requires.patch",
+        "pkg-config.patch", "find_lib.patch", "no-download.patch"]
 
     def get_recipe_env(self, arch=None):
         env = super(Secp256k1Recipe, self).get_recipe_env(arch)

pythonforandroid/recipes/secp256k1/no-download.patch

@@ -0,0 +1,13 @@
+diff --git a/setup.py b/setup.py
+index bba4bce..5ea0228 100644
+--- a/setup.py
++++ b/setup.py
+@@ -55,6 +55,8 @@ except OSError:
+ 
+ 
+ def download_library(command):
++    # we will use the custom libsecp256k1 recipe
++    return
+     if command.dry_run:
+         return
+     libdir = absolute("libsecp256k1")

pythonforandroid/recipes/secp256k1/pkg-config.patch

@@ -1,5 +1,21 @@
+diff --git a/setup.py b/setup.py
+index bba4bce..609481c 100644
+--- a/setup.py
++++ b/setup.py
+@@ -48,10 +48,7 @@ if [int(i) for i in setuptools_version.split('.')] < [3, 3]:
+ try:
+     subprocess.check_call(['pkg-config', '--version'])
+ except OSError:
+-    raise SystemExit(
+-        "'pkg-config' is required to install this package. "
+-        "Please see the README for details."
+-    )
++    pass
+ 
+ 
+ def download_library(command):
 diff --git a/setup_support.py b/setup_support.py
-index 68a2a7f..42e85a3 100644
+index 68a2a7f..ccbafac 100644
 --- a/setup_support.py
 +++ b/setup_support.py
 @@ -40,6 +40,7 @@ def absolute(*paths):