gnu: beets: Fix build with newer Werkzeug.

* gnu/packages/patches/beets-werkzeug-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/music.scm (beets)[source](patches): New field.

gnu/local.mk

@@ -756,6 +756,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/bash-completion-directories.patch	\
   %D%/packages/patches/bastet-change-source-of-unordered_set.patch	\
   %D%/packages/patches/bazaar-CVE-2017-14176.patch		\
+  %D%/packages/patches/beets-werkzeug-compat.patch		\
   %D%/packages/patches/beignet-correct-file-names.patch		\
   %D%/packages/patches/benchmark-unbundle-googletest.patch	\
   %D%/packages/patches/biber-fix-encoding-write.patch		\

gnu/packages/music.scm

@@ -2941,6 +2941,7 @@ Songs can be searched by artist, name or even by a part of the song text.")
     (source (origin
               (method url-fetch)
               (uri (pypi-uri "beets" version))
+              (patches (search-patches "beets-werkzeug-compat.patch"))
               (sha256
                (base32
                 "0m40rjimvfgy1dv04p8f8d5dvi2855v4ix99a9xr900cmcn476yj"))))

gnu/packages/patches/beets-werkzeug-compat.patch

@@ -0,0 +1,18 @@
+Be compatible with python-werkzeug 1.0.0.
+
+Taken from upstream:
+https://github.com/beetbox/beets/commit/d43d54e21cde97f57f19486925ab56b419254cc8
+
+diff --git a/beetsplug/web/__init__.py b/beetsplug/web/__init__.py
+index f53fb3a954..21ff5d94ed 100644
+--- a/beetsplug/web/__init__.py
++++ b/beetsplug/web/__init__.py
+@@ -169,7 +169,7 @@ def to_python(self, value):
+         return ids
+ 
+     def to_url(self, value):
+-        return ','.join(value)
++        return ','.join(str(v) for v in value)
+ 
+ 
+ class QueryConverter(PathConverter):