builddoc: Treat '[pbr] autodoc_tree_excludes' as a multi-line opt

We were treating this a single line, comma- or space-delimited option.
This was incorrect and was causing issues for projects like neutron-lib
when Sphinx 1.7, which switches from optparse to the stricter argparse
was used. In addition, this project was including comments in the
multi-line opt. These were being passed through but Sphinx < 1.7 was
simply ignoring them. These are now filtered out.

Change-Id: I177edf0f44714175da220cf3a960b8f23aa4ab09
Closes-Bug: #1753082

pbr/builddoc.py

@@ -242,6 +242,8 @@ class LocalBuildDoc(setup_command.BuildDoc):
         self.autodoc_tree_excludes = ['setup.py']
 
     def finalize_options(self):
+        from pbr import util
+
         # Not a new style class, super keyword does not work.
         setup_command.BuildDoc.finalize_options(self)
 
@@ -262,8 +264,8 @@ class LocalBuildDoc(setup_command.BuildDoc):
         opt = 'autodoc_tree_excludes'
         option_dict = self.distribution.get_option_dict('pbr')
         if opt in option_dict:
-            self.autodoc_tree_excludes = option_dict[opt][1]
-            self.ensure_string_list(opt)
+            self.autodoc_tree_excludes = util.split_multiline(
+                option_dict[opt][1])
 
         # handle Sphinx < 1.5.0
         if not hasattr(self, 'warning_is_error'):

pbr/util.py

@@ -580,7 +580,7 @@ def split_multiline(value):
 
     value = [element for element in
              (line.strip() for line in value.split('\n'))
-             if element]
+             if element and not element.startswith('#')]
     return value