Do not create patch if there are binary files

"git diff" can accept --binary, which will produce diff with binary content. But patch does not understood
such diff, so we are doomed. Diff with binary file will produce

Binary files /dev/null and b/app/assets/images/false.png differ
diff --git a/app/assets/images/foreman.png b/app/assets/images/foreman.png
new file mode 100644
index 0000000..8815824

And patch will accept such syntax but will not create the file. Not even empty one.
So this result in silently throwing away some changes.

src/tito/builder.py

@@ -828,6 +828,11 @@ class UpstreamBuilder(NoTgzBuilder):
         debug("Generating patch with: %s" % patch_command)
         output = run_command(patch_command)
         print(output)
+        (status, output) = commands.getstatusoutput(
+            "grep 'Binary files .* differ' %s " % patch_file)
+        if status == 0 and output != "":
+            error_out("You are doomed. Diff contains binary files. You can not use this builder")
+
         # Creating two copies of the patch here in the temp build directories
         # just out of laziness. Some builders need sources in SOURCES and
         # others need them in the git copy. Being lazy here avoids one-off

src/tito/distributionbuilder.py

@@ -27,6 +27,11 @@ class DistributionBuilder(UpstreamBuilder):
                % (self.rpmbuild_gitcopy, self.project_name, self.upstream_version, self.build_version, self.git_commit_id))
         self.patch_files = output.split("\n")
         for p_file in self.patch_files:
+            (status, output) = commands.getstatusoutput(
+                "grep 'Binary files .* differ' %s/%s " % (self.rpmbuild_gitcopy, p_file))
+            if status == 0 and output != "":
+                error_out("You are doomed. Diff contains binary files. You can not use this builder")
+
             run_command("cp %s/%s %s" % (self.rpmbuild_gitcopy, p_file, self.rpmbuild_sourcedir))
 
         (patch_number, patch_insert_index, patch_apply_index, lines) = self._patch_upstream()