[XXX DO-NOT-MERGE] erp5: use bstr+ustr as builtin string types

Does not work yet as it currently breaks with

      File "/srv/slapgrid/slappart47/srv/runner/software/7f1663e8148f227ce3c6a38fc52796e2/bin/runwsgi", line 4, in <module>
        from Products.ERP5.bin.zopewsgi import runwsgi; sys.exit(runwsgi())
      File "/srv/slapgrid/slappart47/srv/runner/software/7f1663e8148f227ce3c6a38fc52796e2/parts/erp5/product/ERP5/__init__.py", line 36, in <module>
        from Products.ERP5Type.Utils import initializeProduct, updateGlobals
      File "/srv/slapgrid/slappart47/srv/runner/software/7f1663e8148f227ce3c6a38fc52796e2/parts/erp5/product/ERP5Type/__init__.py", line 42, in <module>
        from .patches import pylint
      File "/srv/slapgrid/slappart47/srv/runner/software/7f1663e8148f227ce3c6a38fc52796e2/parts/erp5/product/ERP5Type/patches/pylint.py", line 524, in <module>
        __import__(module_name, fromlist=[module_name], level=0))
      File "src/lxml/sax.py", line 18, in init lxml.sax
      File "src/lxml/etree.pyx", line 154, in init lxml.etree
    TypeError: Expected bytes, got golang.bstr

in

    cdef bytes _FILENAME_ENCODING = (sys.getfilesystemencoding() or sys.getdefaultencoding() or 'ascii').encode("UTF-8")

    (https://github.com/lxml/lxml/blob/a9f31d9b/src/lxml/etree.pyx#L150)

/cc @kazuhiko, @jerome

component/pygolang/buildout.cfg

@@ -23,9 +23,9 @@ setup-eggs =
 
 [pygolang-repository]
 recipe  = slapos.recipe.build:gitclone
-repository = https://lab.nexedi.com/nexedi/pygolang.git
-branch   = master
-revision = pygolang-0.1-69-g044deb35
+repository = https://lab.nexedi.com/kirr/pygolang.git
+branch   = y/bstr+x/gpystr
+#revision = pygolang-0.1-69-g044deb35
 location = ${buildout:parts-directory}/pygolang
 git-executable = ${git:location}/bin/git
 

stack/erp5/buildout.cfg

@@ -506,13 +506,13 @@ initialization =
 [erp5-python-interpreter]
 # a python interpreter with all eggs available, usable for the software release but also
 # for external tools (such as python extension in theia).
-# we will also want to use bstr/ustr from gpython as builtin string types, but keep
+# we also want to use bstr/ustr from gpython as builtin string types, but keep
 # the program named as just `python`.
 <= gpython-interpreter
 interpreter = python
 pre-initialization +=
   import os
-  os.environ.setdefault('GPYTHON_STRINGS', 'pystd')    # TODO switch to bstr+ustr
+  os.environ.setdefault('GPYTHON_STRINGS', 'bstr+ustr')
   os.environ.setdefault('GPYTHON_RUNTIME', 'threads')
 eggs += ${eggs:eggs}
 extra-paths += ${eggs:extra-paths}