macosx: add patchfile for PyQt5

works around a bug in py2app, which gave errors due to Python 2 code
that should not be executed

macosx/build-dmg.sh

@@ -8,7 +8,11 @@ Prerequisites:
 - Frescobaldi's dependencies installed through MacPorts with default variants,
   for the requested architecture set,
 - \$PATH contains Git, appdmg (a node.js/npm package) and OpenSSL with
-  SHA256 support.
+  SHA256 support,
+- due to a bug in py2app, PyQt5 needs to be patched by applying the patch file
+  patch-PyQt5-uic.diff in the directory lib/python3.6/site-packages/PyQt5/uic
+  of the Python.framework corresponding to the used Python, e.g., with
+    sudo patch -d/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/PyQt5/uic -p0 < patch-PyQt5-uic.diff
 
 It is strongly recommended that no Python packages are active except for
 Frescobaldi's dependencies.

macosx/patch-PyQt5-uic.diff

@@ -0,0 +1,67 @@
+diff --git __init__.py.orig __init__.py
+index 5d7e90a..b9c9ffd 100644
+--- __init__.py.orig
++++ __init__.py
+@@ -189,10 +189,7 @@ def loadUiType(uifile, from_imports=False, resource_suffix='_rc', import_from='.
+
+     from PyQt5 import QtWidgets
+
+-    if sys.hexversion >= 0x03000000:
+-        from .port_v3.string_io import StringIO
+-    else:
+-        from .port_v2.string_io import StringIO
++    from .port_v3.string_io import StringIO
+
+     code_string = StringIO()
+     winfo = compiler.UICompiler().compileUi(uifile, code_string, from_imports, resource_suffix, import_from)
+diff --git properties.py.orig properties.py
+index 3b4af2a..a9a9553 100644
+--- properties.py.orig
++++ properties.py
+@@ -45,10 +45,7 @@ import sys
+ from .exceptions import NoSuchClassError, UnsupportedPropertyError
+ from .icon_cache import IconCache
+
+-if sys.hexversion >= 0x03000000:
+-    from .port_v3.ascii_upper import ascii_upper
+-else:
+-    from .port_v2.ascii_upper import ascii_upper
++from .port_v3.ascii_upper import ascii_upper
+
+
+ logger = logging.getLogger(__name__)
+diff --git Compiler/qobjectcreator.py.orig Compiler/qobjectcreator.py
+index d85182f..c65e628 100644
+--- Compiler/qobjectcreator.py.orig
++++ Compiler/qobjectcreator.py
+@@ -44,10 +44,7 @@ import sys
+ from .indenter import write_code
+ from .qtproxies import QtGui, QtWidgets, Literal, strict_getattr
+
+-if sys.hexversion >= 0x03000000:
+-    from ..port_v3.as_string import as_string
+-else:
+-    from ..port_v2.as_string import as_string
++from ..port_v3.as_string import as_string
+
+
+ logger = logging.getLogger(__name__)
+diff --git Compiler/qtproxies.py.orig Compiler/qtproxies.py
+index e5b7266..5a2870d 100644
+--- Compiler/qtproxies.py.orig
++++ Compiler/qtproxies.py
+@@ -44,12 +44,8 @@ import re
+ from .indenter import write_code
+ from .misc import Literal, moduleMember
+
+-if sys.hexversion >= 0x03000000:
+-    from ..port_v3.proxy_base import ProxyBase
+-    from ..port_v3.as_string import as_string
+-else:
+-    from ..port_v2.proxy_base import ProxyBase
+-    from ..port_v2.as_string import as_string
++from ..port_v3.proxy_base import ProxyBase
++from ..port_v3.as_string import as_string
+
+
+ i18n_strings = []