matplotlib: Update to 3.0.0 (#4434)

Matplotlib is Python 3 only now and has auto backend detection so
move all the backend related dependencies into optdepends.

This splits the package into two PKGBUILD files, one building a Python 2
version providing 2.2.x and one building a Python 3 version providing 3.x+

mingw-w64-python3-matplotlib/setupext.py.patch

@@ -0,0 +1,37 @@
+--- matplotlib-3.0.0/setupext.py.orig	2018-09-18 05:17:52.000000000 +0200
++++ matplotlib-3.0.0/setupext.py	2018-09-20 12:51:06.529116400 +0200
+@@ -22,6 +22,7 @@
+ import setuptools
+ import versioneer
+ 
++MSYS = "MSYSTEM" in os.environ
+ 
+ def _get_xdg_cache_dir():
+     """
+@@ -267,7 +268,7 @@
+         """
+         Determines whether pkg-config exists on this machine.
+         """
+-        if sys.platform == 'win32':
++        if sys.platform == 'win32' and not MSYS:
+             self.has_pkgconfig = False
+         else:
+             self.pkg_config = os.environ.get('PKG_CONFIG', 'pkg-config')
+@@ -946,7 +947,7 @@
+         if options.get('local_freetype'):
+             return "Using local version for testing"
+ 
+-        if sys.platform == 'win32':
++        if sys.platform == 'win32' and not MSYS:
+             try:
+                 check_include_file(get_include_dirs(), 'ft2build.h', 'freetype')
+             except CheckFailed:
+@@ -1176,7 +1177,7 @@
+         }
+ 
+     def check(self):
+-        if sys.platform == 'win32':
++        if sys.platform == 'win32' and not MSYS:
+             check_include_file(get_include_dirs(), 'png.h', 'png')
+             return 'Using unknown version found on system.'
+