doc: add path to 'manpages' to conf.py

Problem: sphinx-build cannot find the 'manpages' module which is in
the same directory as conf.py.

Add the directory to sys.path so it can be loaded.

Author: jameshcorbett

doc/Makefile.am

@@ -427,7 +427,6 @@ stderr_devnull_0 = >/dev/null 2>&1
 
 $(MAN_FILES): manpages.py conf.py $(RST_FILES)
 	$(sphinx_man) \
-	PYTHONPATH=$(PYTHONPATH):$(abs_srcdir) \
 	SPHINX_BUILDDIR=$(abs_builddir) $(PYTHON) \
 		-m sphinx $(sphinx_verbose_flags) -b man $(srcdir) ./man \
 		$(STDERR_DEVNULL)
@@ -440,7 +439,6 @@ $(MAN_FILES): manpages.py conf.py $(RST_FILES)
 .PHONY: html
 html: conf.py $(RST_FILES)
 	$(sphinx_html) \
-	PYTHONPATH=$(PYTHONPATH):$(abs_srcdir) \
 	SPHINX_BUILDDIR=$(abs_builddir) $(PYTHON) \
 		-m sphinx $(sphinx_verbose_flags) -b html $(srcdir) ./html \
 		$(STDERR_DEVNULL)

doc/conf.py

@@ -22,6 +22,11 @@
 #
 import os
 import sys
+
+# add `manpages` directory to sys.path
+import pathlib
+sys.path.append(str(pathlib.Path(__file__).absolute().parent))
+
 from manpages import man_pages
 import docutils.nodes