convert: set LC_CTYPE around calls to Subversion bindings

The Subversion bindings require that LC_CTYPE is set. However, we don’t want to
set it all the time, as it changes the behavior of str methods on Python 2. The
taken approach is hopefully fine-grained enough to not trigger any
locale-specfic behavior of the str methods and coarse-grained enough to not
clutter the code.

Emulating the with-statement behavior in before() and after() should be safe, as
after() is always called when before() is called. hgext.convert.hg takes a
similar approach.

hgext/convert/subversion.py

@@ -187,6 +187,7 b' def debugsvnlog(ui, **opts):'
     """Fetch SVN log in a subprocess and channel them back to parent to
     avoid memory collection issues.
     """
+    with util.with_lc_ctype():
     if svn is None:
         raise error.Abort(
             _(b'debugsvnlog could not load Subversion python bindings')
@@ -420,6 +421,7 b' class svn_source(converter_source):'
         self.url = geturl(url)
         self.encoding = b'UTF-8'  # Subversion is always nominal UTF-8
         try:
+            with util.with_lc_ctype():
             self.transport = transport.SvnRaTransport(url=self.url)
             self.ra = self.transport.ra
             self.ctx = self.transport.client
@@ -477,6 +479,7 b' class svn_source(converter_source):'
             )
 
         try:
+            with util.with_lc_ctype():
             self.head = self.latest(self.module, latest)
         except SvnPathNotFound:
             self.head = None
@@ -494,6 +497,13 b' class svn_source(converter_source):'
             self.wc = None
         self.convertfp = None
 
+    def before(self):
+        self.with_lc_ctype = util.with_lc_ctype()
+        self.with_lc_ctype.__enter__()
+
+    def after(self):
+        self.with_lc_ctype.__exit__(None, None, None)
+
     def setrevmap(self, revmap):
         lastrevs = {}
         for revid in revmap: